@maynarkh I'm willing to believe Hamas does stuff but I do not understand how an oxygen concentrator would even be used in a tunnel. It's standard medical equipment.
No one uses them for ventilation in tunnels, mines, etc!
As for why they were being smuggled, if Israel is blocking them because it thinks they are for tunnels, then no one in Gaza has them, they need them, and can't get them. Smuggling for humanitarian reasons would make sense.