If he had an oil leak evidence will be down the entire chassis. Seriously, if its leaking its got to go somewhere. All motors and develope a problem and start to consume oil. Rings can collapse, head gaskets can go, oil cooling lines can spring a leak. All of them perfectly repairable if idenitified and caught in time.
My guess is that by running the engine at highway speed with low oil pressure likely causes a spun rod bearing or a full ring collapse. Either way when oil is starved heat builds and at some point the heat fatigue takes over and the engine will throw a rod (which usually results in a gaping hole in the oil pan if you are luckly, or a large hole in the block if you are not so lucky.