Unlikely-more like the conditions in which they were kept
What were they ?
Where were they?
Could it have been the watering?
All gone-the whole lot??
But you haven't said where you kept them
We're a bit short of detail here.
I use peat free, seedlings don't die of that.
Growing in warmth then putting somewhere cold,or too much/too little water, that will kill them
As will Damping off disease.
i had problems with seedlings dieing off, they were in my heated greenhouse and i found it was the compost that was the problem it was ok on the top but when you checked below the compost it was all dried out, and the compost was from dobbies garden centre and it was 3 x 60lt for £12 dobbies mult-purpose i now use mother earth multi-purpose compost from local nursery it is 3 x 70lt for £15
I have used peat free compost for several years now, and the only thing that I would say is that you have to be very careful about watering, it does not quite soak as the old composts did - but with care it works perfectly well, unless you get a batch that is contaminated with bad rubbish. We have found wire, bits of rubber, brick bits and all sorts in it, so it does need sieving for seeds and baby plants. I mix it with a good loam compost for special seeds or young plants, when it is fine.