this image file IS tagged with sRGB.
I see it clearly in PS (CC2017). And my settings would have alerted me otherwise.
Maybe the dropbox link confirms this.
The metadata does.
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.6-c138 79.159824, 2016/09/14-01:09:01 ">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about=""
xmlns:xmp="http://ns.adobe.com/xap/1.0/"
xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
xmlns:stEvt="http://ns.adobe.com/xap/1.0/sType/ResourceEvent#"
xmlns:stRef="http://ns.adobe.com/xap/1.0/sType/ResourceRef#"
xmlns:tiff="http://ns.adobe.com/tiff/1.0/"
xmlns:exif="http://ns.adobe.com/exif/1.0/">
<xmp:CreatorTool>Adobe Photoshop CS5.1 Windows</xmp:CreatorTool>
<xmp:CreateDate>2017-10-02T16:28:32-07:00</xmp:CreateDate>
<xmp:MetadataDate>2017-10-02T16:30:12-07:00</xmp:MetadataDate>
<xmp:ModifyDate>2017-10-02T16:30:12-07:00</xmp:ModifyDate>
<photoshop:LegacyIPTCDigest>00000000000000000000000000000001</photoshop:LegacyIPTCDigest>
<photoshop:ColorMode>3</photoshop:ColorMode>
<photoshop:ICCProfile>sRGB IEC61966-2.1</photoshop:ICCProfile>
<photoshop:DocumentAncestors>
<rdf:Bag>
<rdf:li>adobe:docid:photoshop:c827c48c-cf33-117a-abc4-b573f22281ee</rdf:li>
</rdf:Bag>
</photoshop:DocumentAncestors>
<photoshop:History>2017-10-02T16:25:39-07:00	File Untitled-1 opened
2017-10-02T16:28:32-07:00	File H:\Heather Thomas\Heather Thomas\MOPA Brand Products\POSTCARDS\Francesca Oyster.pdf saved
2017-10-02T16:30:12-07:00	File H:\Heather Thomas\Heather Thomas\MOPA Brand Products\POSTCARDS\Francesca Oyster.jpg saved
</photoshop:History>
<dc:format>image/jpeg</dc:format>
<xmpMM:InstanceID>xmp.iid:16055A67C9A7E711A4FBF1657DAE779C</xmpMM:InstanceID>
<xmpMM:DocumentID>xmp.did:14055A67C9A7E711A4FBF1657DAE779C</xmpMM:DocumentID>
<xmpMM:OriginalDocumentID>xmp.did:14055A67C9A7E711A4FBF1657DAE779C</xmpMM:OriginalDocumentID>
<xmpMM:History>
<rdf:Seq>
<rdf:li rdf:parseType="Resource">
<stEvt:action>created</stEvt:action>
<stEvt:instanceID>xmp.iid:14055A67C9A7E711A4FBF1657DAE779C</stEvt:instanceID>
<stEvt:when>2017-10-02T16:28:32-07:00</stEvt:when>
<stEvt:softwareAgent>Adobe Photoshop CS5.1 Windows</stEvt:softwareAgent>
</rdf:li>
<rdf:li rdf:parseType="Resource">
<stEvt:action>saved</stEvt:action>
<stEvt:instanceID>xmp.iid:15055A67C9A7E711A4FBF1657DAE779C</stEvt:instanceID>
<stEvt:when>2017-10-02T16:30:12-07:00</stEvt:when>
<stEvt:softwareAgent>Adobe Photoshop CS5.1 Windows</stEvt:softwareAgent>
<stEvt:changed>/</stEvt:changed>
</rdf:li>
<rdf:li rdf:parseType="Resource">
<stEvt:action>converted</stEvt:action>
<stEvt:parameters>from application/pdf to image/jpeg</stEvt:parameters>
</rdf:li>
<rdf:li rdf:parseType="Resource">
<stEvt:action>derived</stEvt:action>
<stEvt:parameters>converted from application/pdf to image/jpeg</stEvt:parameters>
</rdf:li>
<rdf:li rdf:parseType="Resource">
<stEvt:action>saved</stEvt:action>
<stEvt:instanceID>xmp.iid:16055A67C9A7E711A4FBF1657DAE779C</stEvt:instanceID>
<stEvt:when>2017-10-02T16:30:12-07:00</stEvt:when>
<stEvt:softwareAgent>Adobe Photoshop CS5.1 Windows</stEvt:softwareAgent>
<stEvt:changed>/</stEvt:changed>
</rdf:li>
</rdf:Seq>
</xmpMM:History>
<xmpMM:DerivedFrom rdf:parseType="Resource">
<stRef:instanceID>xmp.iid:15055A67C9A7E711A4FBF1657DAE779C</stRef:instanceID>
<stRef:documentID>xmp.did:14055A67C9A7E711A4FBF1657DAE779C</stRef:documentID>
<stRef:originalDocumentID>xmp.did:14055A67C9A7E711A4FBF1657DAE779C</stRef:originalDocumentID>
</xmpMM:DerivedFrom>
<tiff:ImageWidth>1275</tiff:ImageWidth>
<tiff:ImageLength>1800</tiff:ImageLength>
<tiff:BitsPerSample>
<rdf:Seq>
<rdf:li>8</rdf:li>
<rdf:li>8</rdf:li>
<rdf:li>8</rdf:li>
</rdf:Seq>
</tiff:BitsPerSample>
<tiff:PhotometricInterpretation>2</tiff:PhotometricInterpretation>
<tiff:Orientation>1</tiff:Orientation>
<tiff:SamplesPerPixel>3</tiff:SamplesPerPixel>
<tiff:XResolution>3000000/10000</tiff:XResolution>
<tiff:YResolution>3000000/10000</tiff:YResolution>
<tiff:ResolutionUnit>2</tiff:ResolutionUnit>
<exif:ExifVersion>0221</exif:ExifVersion>
<exif:ColorSpace>1</exif:ColorSpace>
<exif:PixelXDimension>1275</exif:PixelXDimension>
<exif:PixelYDimension>1800</exif:PixelYDimension>
</rdf:Description>
I don't see a problem.
If I place your file unchanged into a document created with the Preserve Embedded policy, the embedded profile shows in the Links panel:
If I export to the default PDF/X-4 the image exports with the sRGB profile. Here in AcrobatProDC: