How to deal with people judging your 'overproductiveness'?
I'm not surprised that hard work isn't considered a convincing answer.  It's not plausible that you are putting in four times as many hours as your peers.  Hardly anyone actually works a hundred hours per week, and even that would achieve a fourfold increase only if your peers are putting in just twenty-five hours.  Instead, it's possible that you are working far more efficiently than your peers, but that's a tricky answer to give.  You'll offend people if it comes across as "I'm probably just smarter than you are" or "you sure must be wasting a lot of time", and you won't look good if it comes across as "I cut corners to try to rush my work into print as quickly as I can".

One common attitude in mathematics is that publishing a lot of papers is a waste of your potential: if you have the time and energy to do that, then you should be spending it trying to write better papers, not more papers.  How strongly this is felt depends on the subfield, so I don't know whether it applies to your area.  To the extent it does, there may be no compelling explanation you can give for publishing a lot of good papers but no fantastic papers.  (If you are publishing some fantastic papers, then you don't need to worry about this.)


  Is there any better ways to explain 'overproductivity' to peers, in a non-offending way, how I publish more (and good quality) papers than the average in my field?


Probably not. Your peers might simply be envious, in which case they already feel bad about the productivity difference and there's probably nothing you can say to make them feel better about it.  (They might need to vent to a friend about how frustrated they are or talk with a mentor about how to improve, but they probably aren't looking for an earnest conversation with you about how you manage to accomplish so much more than they do.)  Or your peers might have legitimate concerns about your approach, in which case no boilerplate explanation will address the concerns and you'd be better off discussing this issue with a trusted mentor instead.  Either way, I don't think you should interpret their questions as genuine requests for information, but rather as complaints.  There's probably no simple answer that will change their minds.