Well, actually, yes it makes perfect sense. Very, very few people have ever played in these open, multi-year campaigns. Even back in the day, it was very uncommon for people to play that way. It's not like there weren't serial adventures back then - GDQ, A1-4, the U series, just to name a few. And, the setup of AD&D lends itself very strongly to retiring characters after name level, that's why you got a keep and all that kind of stuff. That told players it was time to retire.
So, if every time you use the word campaign, you are using it differently than most people around you, you are deliberately obscuring communication. And it's not like you don't know that you are using the word differently than everyone else. Because you've been told repeatedly that no one uses the word the way you use it.
Now, campaign has, AFAIK, no connotations attached to it at all. Negative or positive. I cannot think of any connotative meaning.
Railroading OTOH, has been pretty much universally used as a negative for decades. It's in the same category as Monty Haul, or various other negatively charged terms. I cannot think of a single example where it isn't used negatively. "This AP is a railroad" is never meant neutrally or positively. It's always understood in a negative context.
Now, if you want to keep using a term that you know everyone around you understands as a negative, and then insist that just because you personally don't think it's negative, that's not on them. That's on you. You're causing the break down in communication, particularly when there is a perfectly neutral term - linear - that no one would object to.