The site he went to likely has 'predatory marketing' stating that there was a keylogger present, etc...in the hopes he might purchase their software (Windows-only....but who cares, a sale is a sale to those people) to eradicate such things and make him "safe".
As suggested, just have him clear his cache...reset Safari...whatever needed - probably will function fine afterwards.
If still being slow, then perhaps it is coincidental with his network connection having fits with the network being slow (many students using it!) and psychologically he is just realizing it or being more observant because of the web site he saw.