It happens to everyone, Israel, don't worry — one of the IDF's drones was either shot down or malfunctioned above Gaza. Now Hamas has it.
The video doesn't tell much (talk to us below if you can understand Arabic!), but we do know that it's almost certainly an Israeli drone, despite the country's denial.
That tweet might be denying only that Hamas downed the drone, as opposed to it crashing on its own. Which is entirely possible! Drones go haywire from time to time, and can be pretty crashy. And as The Aviationist points out, the model above is a Rafael Skylite B surveillance UAV, employed by the IDF.
So what will Hamas do with it? It doesn't have the resources for reverse engineering, so, probably just continue to parade it around on TV. Or hand it over to Iran? [The Aviationist]