‘thon’ is pretty common Scots for "that/that one" as opposed to "this/ this one". It's recorded 1804.
"Nonbinary, transgender, and gender nonconforming folks have existed since humans have existed"
Nonconforming folks, all fine and good, but on supposedly "non-binary" folk, theres no such thing.
"Since humans have existed" they have been binary: two haploid cells: sperm and egg, coming together. That's how they come to exist and how they continue to do so.