Yes, you're right and I'm the idiot.
On this image the white vertical strips when present on the flags are on the flagpole side.
The Union flag doesn't really have a 'top' unless you first define which side the flagpole is on.
I suppose with a single-sided printed flag with no flagpole or single white vertical strip, intended to hang against a wall, then it would be conventional to assume the pole is to the left of the flag.