The site is not entirely based on article writing they offers some other attachments like content writing, forum posting(just as they claimed), social media posting, and many other offers but they are all writing related so yes the site needs someone who is proficient in English.I think it is an article writing site according to Mikky based on my understanding.
If this is like blogjob, I can join and earn and practice again if I can still writer longer posts. And do some research again before posting.