Even if his thesis is true, a alternative hypothesis could also be responsible. Electronic voting machines are more resistant to traditional fraud, therefore democrat vote fraud is suppressed.
I had the same thought. Many of the counties mentioned (such as Broward) have Democratically controlled election boards. If there was fraud, it happened under the direct control of the Democrats. My feeling is that there wasn't and that the new machines gave a better accounting of the votes in counties where the accuracy wasn't so good in the past. It is very telling that the liberal Berkley professors don't even consider this as a possibility (at least they don't mention it as being a plausible explanation in their paper).