Just one idea on what might have happened. If you look at it from the manager's point of view, it is probably something like:

Employee told a potential customer that he will make a home-visit, for free. There is no way that the Apple Store would support making promises like that. But if he made that promise while he was at work, it could be construed that he wasn't doing a personal favor, but acting on behalf of his job.

So if anything went wrong (say, he fried the computer) then Apple could potentially have some liability.