Git says "this does not look like a git repository.. exiting" but my commit works anyways

Question

I make a commit:

$ git commit -m 'Add comment'

And I get this message:

env: git: No such file or directory
this does not look like a git repository.. exiting
[my-branch af881ac] Add comment
 1 file changed, 1 insertion(+)

I thought the commit failed, because git doesn't even think there's a repository, but it didn't fail. It worked — I see it when I run git log.

What's going on here?