Tila:
OOC 'Aha it's a hole in the ground that the GM has brought to our attention, let's go look at it' even though we have no idea at all that it might be linked to our stated desperate mission isn't something I understand why we'd do. This is an OOC comment because mostly I'm saying 'let's not metagame'. If there is a faint hint of clue... I'm all for it. Both Elmohater and I have high knowledge skills, and there isn't any hint at all with those skills that says 'going down is in any way related to our mission'
I get where you're coming from, but in this case, it might be helpful to explain my own thought process.
Jak's prime motivator is not helping radaghast, or saving the world, or anything remotely similar. He doesn't really care about the whole good/evil thing. Jak tagged along because it seemed like it might be interesting. While he realizes that the cave is probably unrelated, it is nonetheless still interesting to him, and thus worth investigating, to his mind.
As a sidenote to this, I'd like to point out that even if we did quickly investigate the cave, it's unlikely to have a meaningful delay on finding the entwives(possibility of injury notwithstanding). Thus, I feel the decision of whether or not to investigate is not a big deal.
As for the chance thing, that's just Jak's shtick. He's very much believer in fate. He'll suggest deciding things randomly every time something similar comes up, because to him, whatever the outcome, it was always going to happen that way.