Ooo, not a good sign that the MAF essentially got the sledgehammer treatment, that's a rather delicate component performing the important function of establishing the proper air:fuel ratio. If it couldn't do that, then apart from its own failure (possible, but I rather doubt it), it means the problem rests elsewhere. I wouldn't trust a place that is so ignorant of modern intake systems as not to bother getting an intelligent diagnosis and start fooling with the MAF.
As to the computer, again I'd say it's possible, but doubtful, as you said it was repaired or replaced, and your brother isn't clear on whether the current problem occurred before or after the drenching. Something like that would probably be remembered on the time scale.
If it's possible to do, and you're capable of the work, reset the MAF and start looking elsewhere for culprits. Worst case, you might need a new one and a session in smalls claims court to get your money back from those hamfisted clowns.