Why wouldn't his account show the 3 $2,585 Puts he was long? It's plausible that the 300 AMZN shares may not have appeared immediately, if they were the product of the recent assignment and who knows how that was being handled on RH's end, but the 3 x Long Puts had been purchased in the normal course...why wouldn't they have appeared?
Re-read the OP, you're missing something fundamental. OP's saying the short position was Assigned to the RH kid early (a day before its expiration date). The rule you're citing only applies to what happens at 4pm on expiration day.
Buying Power is separate from holdings and is update instantly. The value of an option position is not added to the buying power. My guess he had about $16,000 cash for buying power, plus the margin. $16,000 x 3 = $48,000 He is assigned about $777,000 worth of AMZN stock. $777,000 - $48,000 = -$730,000 When he checked his account on Thursday June 11 it showed a Buying Power of -$730,000 Holdings are not updated until the next day - but Buying Power is updated instantly. He saw the -$730,000 - but not the long 300 AMZN shares. I'm fairly sure that by Friday June 12 his account was all updated and showing a profit from his AMZN trade.
I know what the OP said. You need to re-read my previous post in this thread. I already covered this "early assignment" scenario. All I am saying is if he chose not to exercise, he could still get automatic exercising provided his options are still ITM at that time. The early assignment is just ONE day before the expiration date. By the next day which is the expiration date, he would've made whole and everything would've been fine.