OP: interesting (if unsettling) story, good decision-making by you and your Dad, and happy ending. It is a classic example of needing to judge each scenario "based on situation and terrain," i.e. on its merits, in its unique context, and I think your Dad deserves a lot of credit for clear thinking.
Let's see: 1:00 a.m., multiple motorcycles, gunning engines, wild firing into the dark. Anyone besides me think there was probably alcohol and/or drugs involved? Further, the origin of the wild firing is at a place that prevents you leaving the area. Finally, you're on high ground and apparently both concealed and with a lot of available cover. Your ace in the hole was a high-powered rifle that could reach out far, far beyond their shotguns, but their firepower gave them a potential advantage in the darkness. Once you had some light, your Lee-Enfield would have outmatched them badly.
They might have been a bunch of kids out to raise hell with booze and guns in the middle of the night, feeling independent and invulnerable with a high macho quotient and quite likely a low judgment quotient. This was not a troop of Cub Scouts out to learn marksmanship, that's for sure! The latter would respond appropriately if they learned you were there. With the former, you just cannot know for sure. If they were a bunch of hell-raising kids, they * probably * would have gotten out of there if you and your Dad gave notice of your presence, but you would have been in a ******* mess if they decided it would be fun to shoot somebody. If they were a gang of bikers, there was an even better chance that they would have caused trouble if they'd known you were there.
You were smart to deprive those guys of any opportunity to screw up--at your expense! Had they still been there at dawn, they might have decided to start trouble, but then the advantage of terrain and firepower would have changed decisively in your favor.