They comb the internet for herp related things they find interesting and link to it. So you must of said/done something interesting enough to peak their interest.
They contact forums and ask if they'd like to be included in their searches, I know BPnet is in the search because my post about snow SD retic made it there as well
I, too had a photo of my boa that I posted on here show up on The Reptile Report. I was shocked when I stumbled upon it but thrilled that they deemed my snake worthy.