Very strange indeed, Tomas! I've never seen any bromeliad seedlings do that. I haven't grown Ae. fosteriana from seed, but I have grown similar species and hybrids (Ae. Bert, orlandiana, correia-araujoi, Can. seidelianum, etc.) and none of them did that.

Tomas,
What kind of light levels are the seedlings getting? I've had some seedlings grow like that if they were overcrowded or underlit.
Paul

Did you notice all of the little pups in the leaf axils, Paul? Stretching is one thing, but have you ever had them do that?

Nope. That is weird! At least no flowers, yet! lol

Paul,

they grow close to the "normal" seedling, so the light intensity should be ok, no direct sun but just shaded from other plants.
Tomas

Tomas,
Keep us posted on their progress. I suspect that at some point, and probably fairly soon, they will assume "normal" characteristics. But if not, you will have something very interesting to share for sure!

Paul