I believe the cause of your confusion is that you assume the "marriage" referred to here (not a literal marriage of course, but a metaphor for a "union") is between the two persons Leonardo Da Vinci and Marcantonio della Torre. I'm not sure that is the case.
Da Vinci is primarily thought of as an artist, but he is also regarded as something of a scientist himself. Much of his work was not simply artistic but he went to extreme lengths to sketch with anatomical correctness. I located the source of your quotation and the overarching theme does seem to be about Da Vinci's sketching accuracy.
I feel that the intended meaning of your quotation is that the relationship between these two men (an artist and a scientist) explains Da Vinci's interest in science and helps to "marry" the two sides of Da Vinci's work - Da Vinci the artist and Da Vinci the scientist.
Therefore it is quite correct to say that this "marries the artist with the scientist" because it is not referring to a union made between two men in the past, but rather the reconciliation in the mind of the reader now of the two sides of the one man.