I doubt it was luck: I rather think it's a completely normal way of affairs. At the moment of discovery, the gas concentration was probably far too low for an explosion. If the house was decently ventilated, the gas concentration may never have reached a sufficient concentration for an explosion. If the house wasn't decently ventilated, someone probably would have woken up from the smell. Gas leaks have a pretty large window for discovery, which is why gas leaks rarely cause explosions. The fact that he was mucking around with the electricity right before it is a coincidence, but it's also something bound to have happened in one of the many gasleaks that happen.