The spittle can contain things that cause the spread of disease, which (as you said) masks help with. And masks with higher specs block smaller particles. So if everyone’s wearing properly-fitted good quality masks in a room, there’s far fewer particles being ejected into the air of that room than if nobody were wearing any masks.

Regarding vaccines, the definitions of things change all the time as technology progresses, so even if it were true that the definition changed, it doesn’t concern me. mRNA vaccines were being researched well before the covid vaccines, but there wasn’t a big push until the pandemic. Without the big push, it can be hard to get funding and such…which can be common in science.