It’s flammable, so there is that risk, yes. It’s not going to explode on it’s own though. You might want to take a look at some videos of people shooting propane tanks. Simply shooting them isn’t enough to make them go boom, you actually have to put a road flare or sparkler (ignition source) near where the gas is going to escape.
I’ve seen people put a cigarette lighter up to the barrel of a gas airsoft pistol, and turn it into a flamethrower. I don’t recommend it, but yeah propane is flammable. Keep in mind though that “Green Gas” is also propane. So I don’t think it’s any more unsafe to use propane than using “Green Gas” bought from an airsoft store.
Actually I’d argue that propane is more safe because of the standardized containers they come in. I’ve seen pictures from players who left one of those “Green Gas” canisters in their car on an hot summer day, and the canister actually exploded. It didn’t make a fire, the gas simply escaped by rupturing the side of the can. It’s less likely that the same thing can happen in the standardized cans, because they have a safety pressure valve that would have simply let off excess pressure in a hot car. (It’s still a bad idea to leave it in your car)
It’s not like a gas mag is going to explode or you burn down a forest when you accidentally turn your airsoft gun into a flamethrower. Those sound like freak accidents, not a typical hazard. Most gas mags I’ve seen have not one, but two failure mechanisms to vent gas in the case of over-pressure. The possibility of explosion is there, but it’s so implausible unless you’re doing dangerous activities like deliberately throwing a full gas mag in a camp fire. I’d say just be aware and be safe.