[referring to the Medal of Honor].
The phrasing in wikipedia makes it sound like he was known to be alive at the time, but one of the citations in the wiki article is " “Boyington, Marine ace, reported alive in Japan”. Ellensburg Daily Record. Associated Press. August 29, 1945. p. 1." , which kind of implies that it wasn’t until August 1945 that he was known to be alive. Another source “Hampson, Fred (May 23, 1944). “Boyington still alive, rumor over Pacific”. Pittsburgh Post-Gazette. Associated Press. p. 5.” says that it’s a ‘rumour’ he’s alive, from May 1944.
Which makes me think it’s more likely than not the Medal was awarded to someone presumed dead at the time (with the usual wartime uncertainly around ‘presumed dead’).