There wasn't a single broker. Each of these banks (8 in total I think?) all let Archgeos separately secure this levered up high-risk position.
The margin call references are quite apt. I believe it was a literal margin call. Goldman and Morgan Stanley forced Archgeos to square up their position, which forced Archgeos to liquidate their stock, which drove down the stock, which left Credit Suisse (who had been hoping for the banks to slowly unwind the position) in a terrible spot.
Period of time when communities and organizations had to turn in their colleagues for not supporting the party. Kids reporting on their parents, coworkers reporting to each other, that sort of thing. It was a period marked by a lot of 'virtue signalling' support for the party.
Highly recommend the film "The Blue Kite" concerning the period (can't speak to the accuracy but at least the creator says its true).