Ok this my new favorite song! I had never heard it before but I love it. It reminds me of Devo and all those bands I liked and watched on mtv in the early/mid 80s. Yes I know I'm dating myself.
I just looked in the booklet and it does credit him with "drums and vocals" on there so I think you're right! He's also credited with that on Compulsive Disclosure (I'm thinking just for that little "Porch" song) but only for "drums" or "drums and lyrics" on the others. He's written that he can't sing/is awful at singing before which is why I assumed it was other band members but that description does fit some of the singing on that album and that song so I guess he didn't let that hold him back. But it's usually Billie or Jason singing and sometimes the others as well so it's not really enough to affect how much I like the singing in general.
It really happened, its from 2012. It's posted in the old instagram thread. I'd forgotten about loads of the random/weird things Billie used to write in the comments.
http://www.greendaycommunity.org/topic/89508-green-day-instagram/page-6