He was gonna say he fed the fries to a house sparrow and the guy waiting around the corner was going to harass him for feeding an invasive species. I guess the joke is that the author sees humans as the most invasive species (which, as an aside, is a bad take when you think about indigenous peoples of our species)
Yeah it's that pedantic nerds that interrupt with sole purpose to point out a flaw is the most annoying.
I get it. It's cool if you know stuff but probably don't make it your point of interacting with people. Most people don't care enough to see that as a positive trait.