Alas an unwise thing to do.
If the aircraft was getting too close to "coffin corner" and/or if there was severe turbulence in the tops we flew through then it was an unwise thing to do. I assume the aircrew would know how severe the turbulence would be via their weather radar and assesed the situation as safe? Can anyone tell me what the buffet margin is on a 737-200adv is at FL410? From what I've read on various web sites, the ceiling for the 737-200 was FL350 and the 737-200adv had a 2,000ft higher ceiling because of improved cabin pressurisation. Perhaps the service ceiling for these variants was more to do with cabin pressurisation than the capabilities of the engines & wing? I'm guessing that a temporary climb to FL410 with the pax and cabin crew strapped-in is unlikely to cause any cabin altitude difficulties for most occupants, but the margin between Mmo and Vmco will be narrower. I'm interested to know how narrow.
The 737-600/700/800/900 variants have ceiling of 41,000ft so perhaps taking a 737-200adv with a light payload to FL410 was more of a cabin altitude issue than a "coffin corner" risk?