I know exactly what he means. It happened to me.
He means sometimes "for no apparent reason" the screen will magnify (more accurately, zooming in to wherever the mouse was/is).
What's actually happening is that his left-mouse finger is tapping. Twice. NOT clicking, just tapping.
Tapping twice again will set the screen back to normal. Took me ages to figure out what was going on there.
It can be disabled in Mouse system settings, but once you know what it is you may not want to do that, as it's quite handy (I just did it to write this message since it's so nice and easy on the eyes). Once I knew what caused it, I opted to keep it and learned not to let my idle finger wander ...