I'm still as stumped as ever about who the HBP is, but I never thought it was Hagrid.
Just FYI, JK said that any part of the HBP story line was erased from COS. She said that the link between the two books had to do with what Harry discovered in the chamber. So I'm thinking maybe it's do to with him pulling out the sword and being a true gryffindor...Who knows!