Check Oxford. You’re not wrong that most laymen use the word in the context you reference, but I’d posit that there’s more accurate ways to describe certain things.

Hypothesis - n. A supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation.

When most people use the word “theory,” this is usually the intended message.

Just to round it over: Theory - n. A supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained.

I wonder if the general utilization of the word sways further and further away from this accuracy, if we’ll see their redefinings. Either way, drives some scientists bonkers