The actual print is far closer to black than the resulting scan, but your theory certainly makes sense. I may have pulled the print out of the developer before it finished. At the moment I'm using a metronome app on my phone for timing (I'll have a real timer soon) and almost certainly wasn't keeping very good track of the clicks before I pulled it.
I'll be going back into the darkroom when I finish making this pizza dough, and trying to print this again without artifacts from me screwing the process up! To say I'm a total newbie at the whole darkroom thing would be an understatement. Last night was the second time I'd ever been in a darkroom.