"Just because ... I can't be ..." [strawman] -- of course it doesn't mean you can't be ... you simply weren't.

"In 1991 it was almost universally referred to as the Internet (capital I): I met only one person between then and now who called it ARPANET."

What "it"? Again, the ARPANET and the Internet are (were, since the ARPANET was decommissioned in 1990) different things.

The Internet is called that because it was formed from interconnected networks, one of which was the ARPANET. The ARPANET did not become the Internet in 1983, it simply adopted the protocols that would later be the basis of the entire Internet.

This isn't worth pursuing further.