He uses his hands, a little head drop device & the leg length check as a cue.

He does many leg length checks, not just a single one as shown on that one video, a single leg check can be off so easily.
If you happen to be laying a bit crooked on the table then the leg lengths will be incorrect.

He has me push my feet/ legs against his hand resistance in each direction to make sure all & hips are as centered as can be.

You lay on your side, he uses the little head drop device and places his hand in the area needing adjustment, and gives a super quick motion and you don't even feel anything other than the little drop table really.
The rechecks the leg length to see if any other correction is needed.