I would think the instructions to the scientist would be to only send a thumbs up if you're confident everything is good. Otherwise, send a thumbs down (or send nothing). I mean, the future of humanity is at stake here.

I also kind of assume that the original mission didn't know about the time dilation thing, but the whole reason to send a human is the human can adapt to a new situation. And in this situation the scientist would realize that thanks to the time dilation problem they either aren't going to be able to respond in the expected (Earth) time frame or to completely half-ass the job they are supposed to do. And they chose the latter, when the former would be very reasonable (Earth might at first wonder about the lack of a response - but later missions would discover the reason why). Though given the experience at the next planet I suppose you can conclude that when they sent out the original batch of scientists they didn't send out their best.

Of course there's also thing with only being able to send out a very basic thumbs up/thumbs down message is a highly contrived thing that's only there to make the extremely weak plot work.