Yes preventative node removal is very common with this cancer (likely NON HPV - oral cancer - includes oral tongue and oral mucousa, and gums) and that's a good thing. (with HPV related oropharangeal cancer and tonsillar, the tend to leave the nodes) I am assuming the recurrence is on the same side as the original tumor. Even so likelihood is they removed only the nodes on the one side. That being the case there is a possibility of it jumping the midline to the other side. If they give you rads - I would request they cook both sides. Your body tends to reorganize things when you remove parts. So it the fluid may drain through these nodes as well.
You have scads of nodes in your neck... they only removed a portion.

best of luck... and hugs...