Dare I try and give maybe a bit of insight based on flying commercial aircraft into/out of US airports a lot??
The US controllers/system often relies on packing lots of flights into tight airspace., TBF that’s increasingly happening elsewhere in the world.
In good weather in the US it’s not unusual for you to get offered a conditional clearance to do something based on you being visual with nominated traffic.
e.g. “737 on finals 2 miles ahead of you for the left, with that traffic in sight you are cleared to land.”. If you see that traffic and you accept the clearance ATC/the controller no longer has responsibility for ensuring separation.
I haven’t heard any of the ATC conversation from last night but one possibility is the controller issued a clearance based on the crew of one of the aircraft seeing the other.
It’s well known that it is hard to judge range and distance at night so one possibility is the crew in one of the aircraft acted incorrectly having misidentified the traffic they were meant to he avoiding.
Also it may be worth knowing anything on a collision course doesn’t move laterally/vertically in the windscreen, so objects on a collision course can be absolute sods to spot by eyeball until very late….
I have no idea if the above issues were a factor in last night but that’s the sort of thing that’s higher up the list of possibilities than pilot’s first flights.
Also there’s been some talk of collision avoidance systems - I’m no longer current but many of the early versions of the airborne warning system called TCAS, that the airliner would have carried, were inhibited from issuing certain warnings at low altitude..
That was because you didn’t want the system shouting at you to “descend”, if that was the appropriate action given the geometry, if you were already close to the ground. That may or may not have been a factor here, don’t know.