Yes, and they Ark crew gave him over to the Grounders to solidify an alliance which they proceeded to break when it was no longer convenient for them. What happened with Finn and the Alliance is exactly the point Pike is making, you cannot trust the Grounders. Basically, we are finally seeing the actions of Lexa bearing fruit. You cannot as a leader give your word and then re-nigh otherwise it makes future dealings troublesome as no one is willing to believe that you will follow through this time.
In fact, Pike's actions make even more sense given what the audience knows at the moment which he does not, that Lexa is dead. Every other clan leader wanted to raze Arkadia to the ground it was Lexa that compromised for only the head of Pike. However, with her death that compromise is on shaky ground as any new commander can recall that deal and push instead for the annihilation of Arkadia. Pike didn't have to start his war with the Grounders so soon and in the stupidest way possible but he is not wrong in his mistrust of the Grounders and his refusal to bend the collective knee to them.
"Our knees do not bend easily."
EDIT:
Great episode by the way, however, I can't say that Pike is in the wrong. Kain's efforts are treasonous and potentially very dangerous.