It's not that uncommon to say "okay" as merely a verbal acknowledgement; I do it all the time! In this context it's indeed ambiguous I guess, but I don't think it can reasonably be assumed to mean "we accept the terms" since where I'm from these type of "verbal contracts" are extremely uncommon – I'm highly skeptical it would have stood up in court (it came as a surprise to everyone that this was enforceable) but we weren't really eager to test that.