Indeed! It may not be proven glass, yet - but, when a fighter is hitting the canvas early in their career against light-hitting opponents, it is absolutely appropriate to raise questions about their punch resistance. I remember early his career, Amir Khan hit the deck against Willie Limond, a small light-hitting fighter, and many of us noted this raised questions about his ability to take a punch. Oh, no no no said all the deniers and fanboys. Well we all saw how that one turned out. Thus, Rodriguez's chin at this point in time is appropriately rated "suspect" or "questionable", and that really shouldn't be the subject of much controversy or debate.
I don't get how anybody could argue that when a fighter gets knocked down by some light-hitting fighter that this doesn't raise questions about their chin. Maybe it's an aberration, but maybe not.