The tongue is certainly the primary. That it is in two places on the tongue is not so common. Anterior tongue cancers are common in smokers, BOT cancers are common in people that are HPV16 positive. The two etiologies for the disease are completely different and not synergistic. So at least for me (and I'm not the guy that has seen the most patients) I have never seen a patient before with two tongue cancers in different locations, that are normally so different from a cause standpoint. Two on the anterior tongue yes, but not one on each end..
Node involvement, especially bilateral like mine, is dangerous. This means that besides going through the normal pathway from the side of the primary to the neck nodes on the same side, it has had time to go to both sides which means it has been there longer. This may be a function of the BOT. That he did not address this earlier, (there surely must have been some discomfort on the anterior tongue) makes me wonder why.
Nodes are part of your body's immune system, and the lymph system that they are part of is connected throughout your whole body. The nodes in your neck to the ones in your upper chest, underarms, mid-chest (mediastial), abdomen, groin, all one big system. So when cancer gets into it, or equally dangerous, the circulatory system, it has free access GIVEN ENOUGH TIME, to metastasis to vital organs far away from the primary. That said, I had very advanced stage four bilateral mets, and everything at the time of the finding was still in my head and neck. Lucky for me, or I might not be typing this. Once it gets out of the local region, (H&N) it is harder to eliminate. I state this so that you will understand this, not to spook you. This is the reason that in work up, he needs scans of his chest for sure, as that is the next likely place for it to go, done. The other place is the brain which he will automatically get scanned when the do the H&N MRI The disease moves at different speeds in different people. Some people it seems to move slowly, some it runs like wildfire. I don't think the doctor can possibly know without scans where it is and where it is not. This is why he needs answers from scans, not the general "opinion" that bilateral staging is advanced (yes) and likely elsewhere as well..... (not necessarily so) - I am living proof that ain't so.