Unnamed character style while flowing docx file in InDesign

I see the same problem on my end. A couple of options...

• In Word, select all the text and press Cntl-spacebar--this will remove all character formatting. Then apply your character style(s) in Word.
• Run a VBA script (macro) to remove unused styles: https://word.tips.net/T001337_Removing_Unused_Styles.html
• After placing, select all unused styles from the Character panel and delete them (your mystery styles are unused). 

I will just note that I rarely import Word files, even simple, clean ones, without phantom styles, color swatches, etc. I think avoiding this "grit" might take more careful file management and editing care than is worth... against, say, just deleting the junk after import.

Which file was first - and which one is a Save As version? 

Doc -> docx or docx -> doc? 

You can also try saving as RTF - in WORD. 

But overall - it's pretty "normal" behavior.