Dragon magic again? Didn't he lose 1 eye the last time he used that?

It was a price for using a full dragon magic. He only use a little bit it here so he may or may not have to pay any price

Wasn't it because he used a specific forbidden spell?

He didn't lose an eye because of dragon magic, he lose it because he used dragon tongue, a language that should not be used by humans

He didn't use pure dragon magic but mixed it with conventional magic