That would depend on how it was being used when the
information was found:
"The tool is to be used to fight vandalism, to check for sockpuppet
abuse, and to limit disruption of the project. It must be used only to
prevent damage to one or several of Wikimedia projects."
This policy would not allow a checkuser on CharlotteWebb
I would guess it was done to check for sockpuppet abuse. Your quote
doesn't say there has to be a reason to suspect something before
checking. The damage admin sockpuppets can do is quite significant, so
it is understandable that someone might like to check.