You didn't necessarily do it wrong, if he's transferring in the US he'd have to collect and recheck baggage (and go through immigration) – I don't think it's possible, at least in my experience, to check through a final destination. LAX immigration isn't usually awful, but two hours would make me itch, even if I wasn't lugging around a bike with a broken arm. Walking between the terminals at LAX is straightforward, just exit and follow the outdoor concourse or cross directly. It's a few minutes a walk between each terminal.
Airport/airline staff may help expedite things for an injured traveller, but it's not guaranteed especially if there's an airline switch (that's the bit you did wrong, because if he misses the flight from LAX, there's no guarantee the airline will transfer his booking, leastways not without financial lubricant), and TSA and DHS follow the beat of their own drum.