Looks like a developing leaf got touched way down inside the new growth bud, Those new growth leaves are really delicate, and just a slight brush with the watering can or a finger while your examining the plant can cause damage like that.

It doesn't look to be spreading to any other leaves, and the rest of that leaf looks healthy. Let it grow in, I've seen plenty of misshapen leaves in my grows. ( I spend too much time down there! )

Keep up the good work! :thumbsup: