Hardly. He said that some spits probably took 30mm hits and lived. Can you prove him wrong? Do you live in Widewing's basement, with complete access to his mountains of data? This image certainly verifies the lethality of a 30mm hit. Can you prove that ALL 30mm hits were fatal? I doubt it.
Burden of proof.
Certainly I cannot prove that all hits were fatal, but asking me to prove him wrong is silly, like asking me to prove that dinosaurs didn't dance.
The shells sometimes failed to detonate, which is not accounted for in AH. However, unless it only sheared off a wingtip, the kill rate for a 30mm detonation on a Spitfire would likely approach 99.9%. That's my educated guess based on multiple examples of photographic evidence, and the Luftwaffe tests that showed 2-3 30mm hits would bring down a B-17.
You're missing the point that in AH when a Spitfire takes a 30mm and survives it takes no damage whatsoever.