** This is incorrect.
The statement, "a human (and or a being or entity that is indistinguishable from a human) cannot walk on water" is NOT an opinion.
If the claim was, "Orion was able to float on his back", this would be a plausible claim. **
This is getting fun...Nope, actually it's not incorrect.
If an event happens in the past, and you have no evidence, you can't make a claim either way (it's true/false, it happened/didn't happen)......
Technically, scientifically, and philosophically speaking, you can't "prove" that "all" humans cannot walk on water....Sure, you can say humans A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, and Y do not have the ability to walk on water, but this does not necessarily "prove" that human "Z" can not walk on water. So, you are technically in realm "H" (see below)...so what do you do? you use your experience, logic and judgement (your observation that humans A-Y can not walk on water) to draw a conclusion about human "Z"-- that they can't walk on water, and likewise you use this to make the further generalization that all humans can not walk on. By the way, I'm right there with you-- I, too, draw the same conclusions...
If there is a claim of something in the past, and you have no evidence ("proof"), you can't make a definitive claim either way....all you can do is simply draw upon your experience, judgement and reasoning to draw forth a conclusion. It doesn't matter what the even or claim is, one is basically doing the same thing.
The only difference is, you prefer to call some opinions and others "proof" or "facts" based on YOUR experience and judgement.
H. If there is NO evidence, here it becomes a gray area-- you use judgement, experience, and/or logic to lead you to draw a conclusion. Technically and philosophically speaking, if there is NO evidence, you can not definitively make a claim either way that something is real or not-- the best, technically/philosophically speaking, you can say is "I have no evidence".