The same procedure is used for dependencies as well as the "calling" package. So, I will guess that whatever the problem was, it was transitory.
While I understand your complaint, I cannot tell, from the information you've supplied, why the initial installation attempt hung. There are diagnostic tools that you might have used -- and because the pkg* tools are written in perl, even perl debugging traces -- but as you now have it installed, I guess it's moot.
Should you have problems with
future package installations, start with pkg_add -v, then consider using top, systat, .... even perl -d if used carefully. This last is described well in
perldebtut(1).