Most fish handle quickly increasing temperatures better than quickly decreasing temperatures... but naturally there is a max level of heat all fish can tank. But I've always understood Clown Loaches can handle warmer tamps better than many others. I would be surprised if 90*F water actually killed them...
What did the fish look like that was dead? I would suspect it died from a lack of oxygen or slight possibility of ick. Temperature swings can definitely invite ick, but I'd be surprised if it died that quickly from it...
According to the time stamps on the posts, it looks like the water took 7~9 hours to cool from 90* to 85*. I wouldn't expect this to be cooling the water to quickly...
Hot hater contains less oxygen, so adding an airstone immediately was great advice, although I think your past the point of that being critical. Although if you have the means of adding surface agitation / circulation, I would still do so.
It also makes sense to prepare yourself to treat the tank for illness. Keep in mind that Clown Loaches are scaless fish and many medications are not suitable for scaless fish.
Best of luck!