I think it is simpler than either parthenogenesis or EUGR. Without 'real world' experience I theorize it is like the mule.
A catgirl breeds with the male human almost always reproducing a catgirl. Whereas the semi-mythical Catman (or Cat-man) is sterile for the most part and rarely breeds with the female human successfully. In both cases the human sire or dam is never available for questioning. Either because they are immediately killed and consumed by the Catiform, or they're just too ashamed to ever admit to it ala the Moped. 
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So catboys are like male calicos, then.
Hard for me to say. Two of the three stray cats haunting my yard are male calicos. Yeah, it really isnt any surprise to me that my world is a little out-of-whack with the 'norm'.
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This thread is starting to remind me of this.
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Of course, that leads to this.
Orc&Pie No.53230 There is an orc, and somehow, he got a pie. And you are hungry.
www.repeat-offenders.net
Negaduck: I see you found the crumb. I knew you'd never notice the huge flag.
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This thread is starting to remind me of this.
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Of course, that leads to this.
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That leads to this! http://splicd.com/1lyP6btIxAk/144/225
NSFW!
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This is Bob Barker remind you to spay your catgirls.
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I'd say you forgot the neuter part, but a catguy hasn't been seen in decades. Which begs the questions: How do the things keep reproducing?
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The one catguy that you haven't seen really gets around.
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or is locked away in a secret breeding chamber, snoo snoo
Clearly, catgirl reproduction is 'all of the above'.