I believe there's two pieces of science here:

1. For at least some, this feeling is related to ADHD medicine. Many are appetite-suppressants (some people are even prescribed Vyvanse only for regulating appetite). So when our appetite is suppressed, nausea is the next thing.
2. Initial hunger often comes in waves. So for those with hyperfoucus we often push through the first wave, and the body gives up in trying to tell us we're hungry. So the thing that actually gets us to eat is again, nausea.