Sorry if I didn't explain it properly - but does anyone else have the text next to the Messages Icon 'com.apple.m...' - I'm not sure it was there the other day!
Probably just a bug. Apps are identified in development (Bundle ID) by reverse DNS notation (com.apple.messages, uk.co.codingcorner.iFont, etc.) so the watch may just not be displaying the app name correctly.
Same for me, Messages from O2 or automated texts from companies come up with that, my contacts display properly though.
Is the sender in your contact list?