Hi
@pakpak! Nope, this doesn't look like a heat stress. It's mostly RH related, in a high relative humidity environment, seedlings tend to show twisted/curly leaves, especially after they've been watered/fed. That's nothing too serious, and it can be fixed by improving your airflow: a simple fan blowing a continous breeze onto your seedlings shoudl solve the issue and help leaves to develop properly. Also watch your waterings and never exceed ~10% of your container's volume, at this early age roots are very sensitive to overwatering. Hope this will help, keep us up-to-date and happy growing 👊