Agreed, though I'll add that on the very rare occasion that my Model 3 does lose the lane lines a bit, it tends to very quickly jerk back into the lane once it picks up the lines again. "it drifted slowly to the left, into my lane, before slowly going back into its own lane" does not sound like plausible autopilot behavior based on my experience; even if it was on autopilot and accidentally left the lane, it wouldn't slowly go back to it's lane, it would sharply correct itself as soon as it found out what happened.