Giant Tube Crab is being lenient by letting you escape after calling it the “metro”.

This is a nice anecdote, and it’s meaningful and valuable in its own right, but it’s not Vonnegut.

The source seems to be this 2020 Tumblr post, where the OP text is someone’s own anecdote following a Kurt Vonnegut extract. I guess someone’s read the post and got confused as to where his bit ends.