Honestly, even if it hit him 2-3 days later, it’d be kind of hard to pin it on the McDonald’s unless he ate all of his meals there that day or there was an outbreak of salmonella in the area and McDonalds was the common factor between the cases.

He could have just as easily gotten it from his breakfast or dinner, and that may even be more likely. I won’t pretend for a moment that McDonald’s employees can be 100% trusted to follow their proper food handling procedures and such to the letter, but I’m certain that a corporate outfit like McDonald’s probably has so many guidelines in place and has idiot-proofed as much of their equipment as possible that it should be next-to impossible for them to be at fault even if half their rules end up getting ignored.

There’s of course cases where things out of their control could happen, like they get a batch of lettuce that’s contaminated with salmonella from their supplier, but that’s the kind of thing that could happen at literally any restaurant, and there’s only so much you can do to mitigate that.