Surely no one was actually thinking there weren't exoplanets though. We didn't need experimental proof that they exist to be reasonably sure that they do.

The existence of exoplanets was an open question still in the 80s. They were pretty sure that they existed, but no one had any evidence of it. It fell kind of in the same category of whether the Riemann conjecture is true. Mathematicians are pretty sure it is, but they don’t know for sure.