Getting captured is not a heroic act. That is the point that Trump was making.
He is only a Senator now because he was a POW back then and he is being hailed as a hero simply for being a POW. But the fact is, he had no choice in his condition. He was captured.
A hero is someone who goes above and beyond the call of duty to save others without any thought for their own well being. There were a lot of true heroes in the Vietnam war. I’m not convinced that John McCain should be numbered among them.
Your post is exactly correct. Nothing heroic about being captured.