Added note: Earlier today, passing by a TV in a public place, I caught a glimpse of Donald Trump in flood-stricken Louisiana handing out...something. It turns out that this "something" was Play-Doh, and that his act pf charity lasted less than a minute. Of course, his presence meant that the Governor of Louisiana had to assign personnel to help provide security for Trump.
I thought that Paul Ryan's soup kitchen episode was the most transparently phony "charitable" act ever caught on camera, but Trump managed to top even that.
I realize that's not exactly an objective web site, but it is the most recent thing I could find about this. I would be very surprised if Trump actually donated using his own money. Also, regardless of whether he helped or not it's pretty plain the motives were primarily political and that his supporters are completely ignoring the fact that Obama was asked not to come (just as Trump was as well) by the governor.
So yeah, regardless of the actual facts, it was a publicity stunt for Trump, first and foremost.