If there's no immediate sign of danger then naturally you won't realise or care. He probably didn't even know it was for a pump, just a grill that could be lifted up. It clearly wasn't pumping that hard if he managed to lift off the grill... It's not about common sense, especially when there was nothing to sense danger to begin with, judging by the BBC video, it didn't even look like it was covering anything in particular, so to a young teenager, he wouldn't know what it was for.

