Yeah, I think the point is that the person answering was wrong/over complicating. If x=10i, then x^2 would be -100 (or potentially -10 depending on what you think the ^2 is applied to).

Depends on what are the allowed values for x are. Real numbers, complexe numbers, binary or I made up my own numbers ;)

The answer in the meme (10i^2) is -10

Probably what they were going for, but there are literally an infinite number of exotic arithmetic spaces you could ask this question in. For example, x=10 works in any ring with a modulus greater than 100 and less than 1000.