(I hope you have got your dose of the black Sunday gold
).
I agree that if you have a preference for a certain back angle (and Im also quite content with a pretty horizontal back angle in the low bar), its good to have a very similar back angle during ascent as descent.
But thats not an explanation why in the ascent he resorted to the stripper squat - you can squat low bar, high bar with various back angles and forward knee/shin travel and not do the stripper squat - or do a stripper squat. So theres another or various other reasons for that.
Imo the most frequent of them are bad technique (a cue like the one i mentioned often help) and discipline to try hard to keep the correct technique and/or maxed quads so that the trainee automatically tries to reduce the moment arm of the quads without extending them against resistance (which is what happens in a stripper squat) - at the cost of a more horizontal back angle.
So even when a more horizontal back angle works - there must be a reason (or various) a more vertical one didnt work: and those two i mentioned happen pretty often.
Short: If he wants to squat with a more horizontal back angle and less forward knee travel, thats fine with me. That may alone get rid off the stripper squat, maybe he still has to cue himself like I wrote. If he wants to squat with a back angle as he showed on the descent (which also looks fine), then he can try the suggestions I gave. Which have worked pretty well so far.