Is this seriously even a question?
Commercial aircraft fly at around 30k ft..
Everest is 29,029 feet max.
The guy is also above clouds.
Use your head.
We are just using the Zetetic method: the earth looks curved, therefore it is.
In this case, direct observation has conflicted with direct observation.
One of the observations is wrong, or misunderstood.
I've been in more planes than the number of times I've been on Everest's peak, so I'm inclined to say that the man was mistaken.
Is that all you can do when you've been backed into a corner?