And in any other situation, you'd be right.
From what I hear, this is an excerpt that Dr. D. made (in 2011, apparently) featuring only the beginning of the sequence from the
"Bing Crosby and his Hollywood Guests" album track that featured Bogey alone singing the song. Crosby got into it later and sang it again with him to amuse the live audience, but that bit isn't part of this excerpt.
...And if that's not enough, it can't really be called an excerpt since the sequence was pieced together for that album track from different parts of the radio show this appeared in.
The only reason they sang it in the first place was that Bogey (sort of) sang it at the end of the movie classic, "The African Queen."