Granted, but -- this is glass we're talking about. It's hard to envision exactly what form it got down in, and I doubt you could swallow it unless you chewed it pretty small, but even quite small pieces of glass can have very sharp edges. I would not be too worried about "grounds," which I'd expect to cause widespread but minor lacerations, but even one piece large enough to have a real edge could be devastating.
The fact that he's still presenting without any frank crashing, having presumably munched his lunch at least 5-10 minutes ago, is reassuring. compared to most of the "potentially unstable" patients we see I'd put him right near the top of the list. Although in most cases I'd agree with a conservative approach, I also want to put on the table the option of a very comfortable medic, with a broad scope of practice and close interaction with medical control, going whole hog -- paralyze and RSI, aggressive analgesia, and any other pharmacology as appropriate to try and reduce gastric motility.
Of course, you could also just park him on the stretcher and haul him off to the ED and maybe 9 times out of 10 that goes well. But remember that the next line in this story could have been, "then he tried to vomit and opened up a six-inch tear in his stomach and died in like ten seconds," and it's hard to say you didn't see it coming. Just some thoughts.
In any case I'd want serious pain management -- just try and imagine this -- and we should certainly be asking the question of why the dude is chewing glass.