What does "use 'hg update' to get a consistent checkout" mean?

Question

I accidentally ran hg update featurebranch while my working directory had changes. When it asked me to resolve merge conflicts on the first file, I immediately pressed Ctrl-C to kill the command. Now when I try to commit I get the error:

abort: last update was interrupted
(use 'hg update' to get a consistent checkout)

What does that mean and how do I recover from this situation?

Answer 1

hg update -r . will do a no-op update to the working branch without changing any files and fix the error message.

_{I'm not entirely sure how/why it works, so if someone explains that I will accept their answer.}