Hi there . First off is he's an oral tongue cancer patient it's highly unlikely he's
HPV + - based on location. Secondly the standard treatment for oral tongue cancer is surgery first (remove as much as possible -or all of the tumor) and lymphnodes -then hit it with radiation and chemo. I'm not sure why they didn't do surgery.
My guess is because of the number of nodes involved and the fact that they didn't operate they are playing it safe since microscopic cancer doesn't highlight on scans, and once it's in the nodes it can travel to anywhere.
Cisplatin - the chemo they use during rads - works in conjunction with radiation. So it's likely a different chemo or combination of chemos they have in mind. Hopefully they'll do some kind of testing to determine which one his tissue responds to.
That said I have to agree with the sooner the better premise.

congrats on the clear scan. And welcome.