In the story he doesn't say what the blinds are but I'm guessing 2/5. So the relevant bets are Player B (Big blind) puts up a $5 blind, Player O (Opener) makes it $20, Player R (Raiser) makes it $50 and player A (All-in) makes it $90, and is all in.
The really bad ruling is that Player R is not then allowed to re-raise. I guess because the all-in bet wasn't "twice the bet".
The actual rule is that a raise must be at least the size of the last raise, not the size of the current total bet. The $50 bet represented a $30 raise, so Player A could have made it $80 and that would qualify as a raise.
This is misunderstood by so many dealers that I don't even bother to correct them anymore. I've just given up on the whole concept of expecting competent dealers.