This is perfectly normal. A camera original file's photo capture date and file creation date naturally start out the same (camera Raw, camera JPG), but that does not apply for other file versions which are later derived from the same photo. The date / time an export was created / modified are accurately stated when you view the file properties, because those have only to do with the individual life history of that file. Factually, it DID come into existence only when the photo involved was exported from LR. That has nothing to do with any picture metadata also involved (such as the known date that the photo was taken, or the camera info, etc). Such picture metadata is independently recorded within the exported image and gets automatically picked up in various contexts. For example, your OS (Mac or Windows) offers some sort of a Photos gallery app. This has the option to group and sort photos by when they were taken and does this automatically, using the embedded metadata, regardless of on what accidental date they were variously exported from LR, or otherwise modified, as shown in their file properties . Or if you upload (say) to online picture hosting, it's relevant info about the photo and the camera which gets extracted and shown; not technicalities about the file. Also your OS file browser can be set to show the Date Taken for picture files, as well as various other metadata. Or you can use some sort of picture viewer utility which prioritises that sort of info. That said, it is convenient for exported files to sort chronologically by capture (not by export) and regardless of which camera they were taken with, across all contexts. One easy way to achieve this is to prefix the filenames of all exported files, with their capture dates in standard form. This can be set up via the Lightroom Export dialog and the renaming options dialog. My own exports from LR are in the form "20171030-[camerafilename].jpg" where the YYYYMMDD format sorts correctly and tells me instantly for any photo export, on what day it was shot. And the format of the [camerafilename] is distinctive of which camera was used; and the camera's image numbering that is embedded within that, makes sure the reference is unique.
... View more