“By their new definition of vaccine, anyone getting sick on purpose with anything is now “vaccinated” against it.”
That’s basically the idea behind the old practice of “chickenpox parties”. People exposed their kids to chickenpox with the idea that once they got over it they would have immunity.
It’s just not a particularly smart idea if the virus in question is dangerous. Vaccines are intended to give you the same result, developing antibodies, without exposing you to the risks of the wild virus.