It seems the NoDeal-petition is much older. It ends in April, and the Remain-petition ends in August. According to the web site, petitions run for 6 months. So it certainly isn't a counter-petition.
They were started with different context, and the remainer petition might only have traction atm because it is new.
Anyway - yeah, let's just decide everything with online petitions. Totally legit.
Does your site cache the numbers? It could be really useful to take some of the load off the main petition's site, as people keep going there and refreshing the page which is overloading it.
I've just been sharing your site URL around on Twitter quite a bit, but it seems to have broken it! If it doesn't have caching already, would be good to add it!
(Pending API availability)