Yamato got captured because he was trying to keep others safe. I'm sure he could have expanded and impaled the snake, but he probably asked himself, "how do I turn this frown upsidedown?" He'll probably use this to his advantage and start som surveilance of his own. He can grown a wood clone from any exposed part of his body and we saw in the last chapter He can grow wood without the use of seals (since he grew that block from his side to push that guy). I think Yamato can escape whenever he wants however he will have to wait for the right time.
Optimistic...really optimistic..