I'm not sure why you converted to mph when everything is already in feet. 1 round is 6 seconds, so the trap triggers in 1/4th of a round. They should have been able to move 75 ft between triggering the trap and it going off. If they were going full speed. I know that's what you said, but i lol'd at you going through MPH. The trigger itself was probably in the middle of that 40 ft circle, so the lead person would only have to move another 20 ft. Were they in initiative at this time?
Not trying to re-litigate it, just curious about the nuts and bolts. Being a magical trap, I assume there was no audible warning. So when it triggered did you put them into initiative and give them a quarter turn to prepare? Just stop them and ask where everyone was located. If there had been a warning of some sort, they could have had a chance to run away.
there's a certain point where the "reality" of dnd has to take a backseat to "you triggered a trap, take x damage"
i mean, i appreciate being curious about things after the fact and wondering if there's different ways to execute things in a smoother manner, but like grabbit said, he's not trying to play csi here and get bogged down in the minutiae of it all.
i'm sure he knew the marching order, that's pretty standard fair in dungeons/dungeon-adjacent terrain and if they trigger a trap, you don't want to give them time to avoid it, that's what the saving throw is for. the time for them to avoid traps is BEFORE they go off, and if they are flying around at 300' per round, then you can assume they were NOT doing their due diligence in checking for traps and whatnot.
it just serves as a lesson that players are strong, and in plenty situations are pretty hard to kill, but the wrong combination of spell and encounter can ROYALLY screw players no matter what level. wind walk gives damage reduction (i think like, to everything but psychic? it's been a while since i looked at that spell) but because the nature of it turning you to basically clear gas means that people think of it as an "i win" button but there's all kinds of issues when you use that spell as anything other than a type of fast travel.
i wouldn't OVERLY punish the players for using it the way they did, it feels like a smart move, but there's no one spell in dnd that should autowin an entire dungeon all by itself. good planning and execution can make the intelligent use of a single spell go incredibly far, but the spell in and of itself shouldn't just win the day.
edit: and i mean... i think initially when we all read what happened we were like "wait, what?" but the more i think about it, the more i side with grabbit. he said it had a magical trigger to it, at least on some level, so yeah, sure, i guess whatever. but no. no think about that. they were moving at 300' per 6 seconds. as wind. that's gonna set off all kinds of physical things. maybe not a weighted pressure plate, it is absolutely going to cause a bunch of physical distortions enough to trigger traps.