There is an ongoing discussion on the effect of caffein on sperm quality. There are articles which describes a possible route for DNA damage to the sperm from caffein https://www.cureus.com/articles/109365-effect-of-stress-and-.... From personal (lab) experience there is a clear difference to the smell of sperm from a coffee to a non coffee drinker, so it ends up there somehow. Whether it truly has an effect is still being discussed.
He didn't specify difference between de-caf coffee vs regular - only coffee vs non-coffee - so might be something other than caffeine that effects smell?
Coffee contains a large number of aromatic components that could be transferred to the semen. Just the way methyl mercaptan from asparagus can be transferred to your urine.
