They reduced the EXP requirement for all skills. It makes sense it levels up at once now. Its not gamebreaking, i think it is to Equalize what skills you would have gotten if you got the exp requirement reduction.
It's an interesting thought, but how can we rationalise the screenshot above where athletics for a companion rises 111 skill points to level 294? Or my friend whose swordman companion went up to the skill cap in two-hander. It is impossible to find any vanilla companions with that kind of skill, so it is clearly cheating. My scout showed the same thing; skill rose above the learning limit in excess of 100; clearly consistent with a bug an not balanced progression.
This would be okay if there was an option to reset all the companions in taverns so we could get rid of the glitchy ones and acquire fresh ones. Alas there's not.
Edit:
Upon further inspection, I think you might be right.But clearly the patch is raising skill levels and not adding the EXP. It should add the exp ontop of the current level, which for our already-high characters should make a very small difference.
Still, not gamebreaking, as you say.
Edit: continued testing the old save. Skill levels have gone from~200 that companions started with to
extremely high levels ~340, which to my knowledge should not even be possible? It seems very much like a bug. I would have never attained that during normal play.