Yes, I think your coworker is right:
Kabocha - Wikipedia
en.wikipedia.org
I've never seen this squash before but it definitely doesn't look like an acorn to me. Based on the photos in the Wiki entry, the acorn is rounder and the outside ridges come to sharper peaks, and there's a single seed cavity instead of 2.
My wife likes acorn squash and I usually grill them cut side down to put on some grill marks and bring out the natural sweetness, before flipping them over, loading the cavities with ridiculous amounts of butter and letting them cook until tender.
Based on the photos in the Wiki entry, the acorn is rounder and the outside ridges come to sharper peaks, and there's a single seed cavity instead of 2.