He means hot as in too much nitrogen/nutrients.
Not all seeds are perfect and if you can see some new leaves coming in the centre, there is still hope for this seedling.
There is nothing you can do but wait to see if it continues to grow.
As I said, not all seeds are perfect and some just don't make it and this may be one of those........but hopefully not.
You will know in 2-5 days time if it is going to develop properly or not.
Sometimes they start off like this and then the next set of leaves is completely normal, so time will tell.