Top-level players regularly are in the 90-95% range aggregated over many games, with spikes up to 98-99%. If you have 98 or 99% accuracy over the course of an entire game (which happens sometimes!), it's either very short or you had significant sequences where you were 100% accurate. If that happened in one of my games it'd be clear evidence I was cheating, if it happens in a Magnus game it's him correctly calculating a complex line and executing it, which he does pretty often.

Edit: Even lower-level cheated games are rarely 100% accurate for the whole game, cheaters usually mix in some bad or natural moves knowing that the engine will let them win anyways. That's why analysis is usually on critical sections, if someone normally plays with a 900 rating but spikes to 100% accuracy every time there's a critical move where other options lose, that's a strong suggestion they're cheating. One of the skills of a strong GM is sniffing out situations like that and being able to calculate a line of 'only moves' under pressure, so it's not nearly as surprising when they pull it off.