Residential proxies exist. Even if they had picked up that the IP was from somewhere else, a decent lawyer could probably have been able to convince a jury that just showed intent because he was trying to conceal his IP.
You'd have to show some evidence that he did conceal his IP, otherwise there should still be reasonable doubt. You can make up whatever you want without evidence, proving it is different.
You're talking nonsense. Among other things, had either the prosecution or the defense seen that the IP addresses didn't match, they would have pursued it further. "The IP addresses don't match but that just proves that the defendant tried to hide their IP address" is a ridiculous corrupt argument, one that a decent prosecutor would never make ... please do not ever serve on a jury.
I'm not sure they would have pursued it much TBH. It seems an incorrect username match was already a slam-dunk for the jury. Even if the defence had seen that the IP address was in the wrong location, the prosecution would argue they'd use a residential proxy. It'd be hard to prove or disprove, so it'd probably impact the jury about the same as the IP address being totally in the wrong region - i.e. it'd not be the magic bullet to show his innocence.
