There is no doubt a very polite and kind way to describe Colin's issues. However, the mun is not on Zulf's account Paarthurnax prefers honesty when it all comes down to it. So he says it rather plainly.

"He is our engineer, and he has a brilliant mind in regards to many things. However, social skill is not amongst his talents. I have found him to be a good friend when such maters can be dealt with."