Earlier quoted context omitted.
Here's what I suspect happened: Any contract requires consideration. Without it, it's not a valid contract. It doesn't require fair consideration, so a clause giving e.g. $1 is typical for many contracts. They were nice and bumped it up to $20. I suspect your work DID belong to the company already, under work-for-hire doctrine, but an explicit contract avoids that ambiguity. Ambiguity can be bad and super-expensive,…
Watch out for "work-for-hire doctrine" erm... assumptions. Last time I looked work-for-hire law only takes effect if there is explicit mention of the term "work-for-hire" in the contract, otherwise it's not "work-for-hire". And I have never seen a contract actually mention "work-for-hire". Do current employment contracts state "work-for-hire"?
So that a conventional employee is covered, but a contractor / consultant with a separate business probably isn't.