He only use it in the "custom logo" section where he showcases his works. Since he's one of its designers, according to https://bower.io/docs/about/, I believe it's fine.

He's the creator of the bower logo. It baffles me that you excluded the most obvious reason before ranting.

I would hardly call my question ranting. I figured it was possible the author had created the logo, but I didn't know for sure.