Hamas has performed charity. But that's not the same as being a charity - their express purpose from their founding has been the destruction of the state of Israel.
That's in reference to Islamist predecessors of Hamas, not the org itself. I'm speaking of Hamas after its founding, which Israel has spent decades funding
Back in '98, which that article discusses, Hamas was not in control of Gaza. This started long before Hamas was a serious contender to Fatah's dominion over Palestinian politics.