This came up in #2083871-19: Allow menu blocks to be placed from the menu page by @yoroy:

I wonder if it's useful to keep referring to a menu as a block. I.e. the action says 'Place block'. Would it be more clearer if this read 'Place menu'? Same with the messages: I'm working on a menu here, but it's being referred to as a block.

This might apply for other block placement pages and we might wanna generalize the implementation to apply in all cases, so assigning to block.module instead of menu.module.