Thats exactly how I took it as well. This didn't seem funny but just cringey.
Today we found out, it would have indeed been hilarious. (But yes, a dick move)
Wearing shorts is "unprofessional". Why? I don't know. I sling code, pants aren't helping or hindering with that. I grabbed shorts this morning, let's not make it complicated.
The fake mustache and joking about didn't make it seem serious at all. He should've just annihilated the interview.