That's very old info, and hasn't really been true for at least 10 years, probably longer. If you want to be REALLY picky, you could say at least since Apple introduced Mac OS X, which dropped the resource/data fork aspect of the filesystem that tended to cause so much trouble in the OS Classic days. But that's still been at least 6-7 years now.
These days, Macs are probably better at sharing info with Windows than Windows is, since Macs tend to be a bit more friendly with older versions of Windows on account of all the open source tools Apple borrowed to make Mac OS X.
What can happen, and seems likely in this case, is that if you don't eject/unmount a removable drive before actually removing it on a Mac, it can cause filesystem corruption. Windows is set up, by default since XP, to sacrifice speed for the convenience of being able to just yank drives whenever you want. An option I would like to see on Mac OS X myself.
If I'm correct, and that's what happened, then Mark is correct about the solution, just not the cause. You'll need to format the drive and basically everything on it will be lost. You'll also want to mention to your son that he needs to eject USB flash drives, HDDs, etc, before unplugging them from his Mac Pro. He should be getting an annoying popup warning every time he does this, but some people have an amazing capacity to ignore things. The check engine light could be on for weeks and they never do anything about it, and then what might have been a $100-$200 repair ends up becoming the need for a new engine. So, unless your son was running Windows at the time, he needs to be sure to eject every removable drive from the system before actually removing it. This can be done by dragging the icon for the drive from the desktop to the trash, or pressing Command+E when the drive icon is highlighted. You can also click the little eject icon next to the drive listing in the lefthand pane of any Finder window. When it disappears from the desktop, or the Finder window, then you can remove the drive from the system.