Twitter users alone is a small sample, but I think there are other anecdotal samples that support (but can't prove) the author's hypothesis. I can't remember anyone talking about PlentyOfFish, and this includes people who have tried multiple dating sites. Compete, Alexa, Google Trends and other traffic estimators also show Match having higher traffic. The only statistics showing PlentyOfFish as bigger than Match are the comScore numbers quoted by Mashable.

It's also important to remember that Markus Frind was accused of overstating the PlentyOfFish traffic levels to generate buzz years ago when the site first became popular. Although the post went off into a satirical conspiracy, there could still be something fishy going on.