Me too, and it is VERY annoying. In my experience, I THINK it has something to do with the order of units in your party, and what groups they were attached to. I noticed that when my companions are up top and in group III, on the field, he correctly says "Cavalry" for group III. However I swear the game randomly switches my companions back to group I at times, and others that even if they're labeled right it doesn't do anything.
Also, I know for a fact that Bannerlord overrides some units group designation and sticks them with others. My companions have been labeled in group I, the infantry, but in battle they get selected by F3, not F1. I BELIEVE that this contributes to our issue.
It's almost like the game goes down the party list and the first person who has a horse is what it uses to "voice" the group shouts, I.E. if I have a mounted companion who is labeled "I" for some reason, it says "Infantry" when I select F3 (even though he's grouped in "I" on the Party Screen, mounts seem to override as I said above). Usually archers are fine, but sometimes they've been messed up. Usually group IV, the horse archers, work without issue, and are the most reliable.