I believe so. I think it's just ghc installed, though. Curiously enough, it also went on to download mesa. Probably a similar mechanism at work there.
The only mention of hooks I see in the manual, though, is referring to the daemon's build hook used for offloading. From what I see, though, I'd assume that they are probably run in a way that errs on the side of "better to run when unnecessary than not run when necessary".
This seems like a fairly common experience - "I ran foo and then it did WHAT?". "guix graph" is really useful, but the parts that it can't explain, it'd be nice to have documented. Where can I read more about these profile hooks, that I may pursue this?