This exact thing just happened to me! Never seen it before.
They’re definitely not discretionary hyphens. I have Invisibles turned on in Word and everything looks completely regular. The words are all followed by a space (blue dot) and there are no special characters, but when pasted into InDesign, random hyphens suddenly appear.
File > Place doesn’t work for me in this situation, as the Word doc’s text needs to go into multiple text boxes in the InDesign doc.
That said, I just used File > Place to import the entire Word doc into a text frame in InDesign, then deleted it all, went back to Word, copied the one paragraph I needed and pasted it into InDesign and this time there were no hyphens, so maybe just doing that resolved the problem? Like, it reset the import variables or something? I’m updating the text in old InDesign docs, overwriting existing text with established paragraph styles, so maybe it’s some legacy issue that’s causing the problem?
Anyway, something for me to keep an eye on!