Man, you need to re-watch the last couple episodes. It started off with them taking the guy he dropped off for a hiking trip. He got kilt in the tests. I'm pretty sure they even mentioned some other unexplained disappearances of inhumans, but that guy was the first one they found dead. Late in the last episode, he told skye he couldn't take her to save sparky because he was pretty sure they had a way to track him based on all the disappearances.I remember them tracking Gordon, but they didn't say anything about picking up the people he dropped off. He would have KNOWN if all the people he was dropping off were getting snatched by Hydra, and thus would have known that they had figured out how to track his quantum entanglement. They're just talking about research subjects in general, they aren't talking about Inhumans specifically. His comment about the Maximoffs being the only survivors makes perfect sense in that context.
And for the record, I meant the last couple that took place before the movie. I think there was another episode last night that I haven't seen yet.