No, it's about tiny and usually unnoticeable delays in hitting a note or a beat. There's nothing incorrect about them. They are not variations either, just tiny mistakes that happen to _all_ humans when they play an instrument.

The assumption that these variations are mistakes is the incorrect one.

There is even research showing the variations in timing follow large macro cycles.

None of this is random or mistakes when we are talking about high level players.

Some is deliberate. Some is totally unconscious.

But not mistakes.