Just a shot, but maybe there was not enough air around it at the sill window open or not. If the air was just standing around with no breeze those temps could cause some havoc, it might have been even hotter indoors around the plant. That combined with the heavy dose of water might have been a lot of stress for seedlings because the mix around the jiffy pucks looks tight as well.
They look stretched for light too, if you can get them to bounce back consider adding some perlite or vermiculite or something to the mix you have to give the roots a better chance at breathing, especially if the plants will be in extreme temps. I am growing in very hot temps using outdoor/indoor balcony. Getting looser soil and keeping a lot of fresh air blowing has been very important. Good luck.
