Naah, it's not at all important. It's more curiosity than anything, really - just a case of recognizing something or someone, but being mildly annoyed by not being able to recall where that thing or person is familiar from. I don't know, this is probably something which only happens to me and a few others and bothers most people not at all, but I like being able to place stuff in context.
As far as I can tell from watching Trinity and Beyond, though, the informational film in which this narrator appeared would have been produced in or around 1956, and the included excerpt (beginning at about 62:00 in the documentary) dealt with the subject of radiation and fallout, as well as with methods of monitoring same and measuring its effects on humans. The person who forwarded the screencap to me said he thought that the narrator could easily have been a model for Sterling Hayden's General Ripper character in Dr. Strangelove, and that's not a hard thing to see - their voices and speech patterns are pretty similar (though the narrator's voice reminds me even more of James Coburn's.)