Palestine Today published this video showing young arson terrorists preparing a set of balloons tethered to burning materials to fly to Israel to start fires.
Notice that there is a cloth covering the helium tank.
My guess is that the helium tanks have markings on them either identifying them as coming from a specific hospital, or with the name of the NGO that donated them for medical purposes.
The people making the video didn't want the world to know that Gazans use helium that was earmarked for medical purposes for terror.