Given the amount of surveillance and satellite tracking blanketing the globe; how can 'someone' possibly send a rocket all the way to crash into the Moon, without anyone noticing, until after it got there?
It bounced. If the structure was pressurised stable form, it was springy once unpressurised. Or maybe, it calved in-flight. Outgassing or explosive failure of something like a pressurised attitude jet, or a fuel cell with volts