Strawberry Pie indoor FustBuds

I would say overwatering and a humidity that is too low. Watch out with those low temps, can really stunt your grow. Which soil are you using anyway? It seems to me that it has also been fertilized a bit too strongly. Light mix soil is best for seedlings.

It doesn't look overly concerning but I'd say its over watering if anything. Young plants have small roots and don't need watered as often or as much as more mature plants. Wait until your pot is obviously lighter when you pick it up before you water again and see if it doesn't straighten back up for you.