That depends upon which prism you view it through. Technically, he was. The only reason we all know the story of Senator John McCain is because he was captured and held as a prisoner of war. Had he merely served his term out as so many other Vietnam veterans that never received any notoriety had, he would also be seen in the same light. Despised by so many at the time they came home, a necessary evil to others. Only a small segment of Americans viewed America’s war fighters as heroes regardless of the circumstances.
Of course Trump blew the delivery. Those who speak without a filter are not long for politics. Not when we live in a world in which candidates are elected for the shallowest of connections to a voter. He had to make the stupid comment that he doesn’t like POW’s which blew any shot he had at pointing out that heroes come in different flavors. Some accomplish great victories in a war theater. Others suffer greatly. Getting captured is seen by some as reason for scorn, not elevation to heroic status. Regardless of where you stand on the merits of McCain and his hero status, Trump botched the way criticism must be handed out in a campaign in which opponents are ready and waiting for a slip up.
There are a significant number of ex-servicemen who fall into this ‘gray’ area category in the minds of some. Including yours truly. I never saw war during my tour. Doesn’t mean I wasn’t ready to fulfill my oath. Some will say our nations first responders are more heroic as they tempt fate all the time. Others will say if you enter into a hazardous job with your eyes wide open you shouldn’t expect any special praise.
What qualifies as heroic varies widely. However, Trump has no authority to lecture others as to who rises to their standard for a hero. In a long campaign, it will be forgotten about as time goes by just as Trump will be once his 15 minutes runs out.