It's usually a cheater. If it's a short game, probably not. But if it's a game 40 moves long, very suspicious.
99.4% accuracy for 500 rating

If he memorized gambit and you fell for it, probably not a cheater. If it was a game that lasted for several moves he probably cheated.
Joined Chess.com for 6 weeks and got 500 in rapid, I'm happy with that.
I just lost a game to another 500 rating player. Losing is fine; I got 73%, it reflects my strength. But my opponent has an accuracy of 99.4%. How's that possible for a 500 player attaining that level?
Intriguing.