^^^ LOL--I don't even know what the word means in this context. Anyone?
God, are you that young?!
As pointed out it's a word that was used for a big error or blunder, arguably it can still be used for that but it being used as a euphemism for an erection is certainly more popular.
The erection angle was certainly around in the 60s when this comic came out but the error meaning was still a bit more popular. This site:
...outlines the story ("boner" is used around 40 times in the story.) The webmaster theorizes that the story was written with this many uses of the word (which was absurdly over used for a short story in an multiple story book) as sort of a "thumbing of the nose" to the CCA.