This is most excellent news.
I see little point in holding back now. Chamsuri has served well and done all we could hope for and more. The most important thing with the exploration was to find a contact, and he (she?) did. Anything from now on is just a bonus.
- Going back to try some other crossing seems just not worth it, why risk another three turns at sea when we can have a new Curragh out soon to do it instead? Just stating the obvious here.
- Holding in place means Chamsuri is safe, but what's the gain? The only possible gain I see is that we deprive FREE from the chance to explore in our direction. But do we really care? Why not let them sink a few curraghs on that? Also it likely won't stop them from seeing where we are from, on their turn they will likely move into a spot from which they see us. And even if they did not, again would we care?
- Going forward means risking probably one more turn in hostile waters. It would make sense, looking at the map, that the jungled coast we are seeing is indeed the FREE lands. So by going ahead we have a 50% chance of not gaining anything (but not much is lost either), and a 50% to be able to gain valuable map knowledge, very useful in trade negotiations.
I think the case is clear for pushing onwards.
EDIT: Thinking some more, there is also a slim chance that the curragh we're seeing is also out exploring someone else's home turf. By pushing on we'd know for sure.
On their techs, they could easily have more techs that we won't know about since we don't have the prerequisites. If they have CB (probably popped from a hut) then they could have Myst too and we wouldn't know. And since they have BW that we don't, they could have IW.
Negotiations should start immediately. They are the other peacefully scientific civ in this game, they are exactly the civ we wanted to meet. We should negotiate a research pact and cartel, so that we don't duplicate each other's work, and that we don't sell techs onwards. They will most likely be interested in this, since they won't see us as a threat. We should also try to glean whether or not they have other contacts, unlikely as it may seem.
This is oh so exciting, we could be the first to make contact anywhere in the world, that will give both our nations a great advantage if it's true.