It is in fact exactly what it say; promotion history is not filled out :) He is missing who promoted him to purple belt. It will also be notified for him on his profile that this is what he needs to fix.

We recently (a few days ago) implemented a check that "promoted by" field must be filled out on every belt in order for the promotion history to be considered complete. One could argue that this check should have been implemented long ago, but some things slip now and then and especially this one was hard to notice, since it's not very often people skip that field :)

Oh right will that mean people will have to reverify him? He just got hit by bad timing I guess

Yes, everyone will be notified about re-confirming their votes.

Not so much bad timing as he just didn't fill out a proper promotion history to begin with :) :)