The fact that some guy taking a selfie on Mt. Everest used a fisheye lens is not exactly a devastating argument against the Earth being round - if some idiot used the photo as "proof the Earth is round" then yeah you've got proof that they're either an idiot or it's a joke you're not getting, but that doesn't exactly prove anything.

But what you do have there is a compelling argument against every flat-Earther who asks "why can't we see the curve?" - I mean, anyone can tell them that at relatively low altitudes there really shouldn't be much of any visible curvature, but this is a really good illustration of how low your expectations should be for e.g. the curvature in weather balloon photos.