Unless he had a difficult time cutting and rehydrating. I don't know what his walking around weight is, but he always looked big. Not rehydrating all the way affects punch resistance.
Fighters like Munguia don't last long for a reason. As it is now, questionable is fair, but I wouldn't call it that looking back over his career.
He is easy to hit and has been dropped multiple times. This time from a feather fisted opponent. This time he went straight back and head bounced on canvas. Back of his head hitting canvas was what knocked him out. .
I would say Munguia's chin is questionable because of how many clean shots he has absorbed over most of his fights. His straight forward tactics have brought him this far but might be catching up to him. Aside from that I don't think He belongs in Super MW. The Frenchman was naturally just too big for Munguia and the Frenchy was able to absorb his shots. That will just replay itself if he stays in that division. Imo Munguia should go back down to 160.