The final boss thing is just unlikely to be something you would happen to try out, so i agree with that.

That’s interesting because I actually do not recall the Cave Johnson line in game because I sorta tuned out a lot of the Cave Johnson lines on my first playthrough. So when I saw how the final scene played out, I sorta just took it as “well screw it, this is a desperate situation, why not just try anything and see what happens?” kind of decision. I didn’t see that action as being foreshadowed by an earlier line but it still made sense to me.

Basically, I think it makes sense for Chell to try that out even if she couldn’t hear Cave talk about that thing.