Can someone tell me about this team? how well known is this team in London? curious if the majority route for Sutton United in London?
I was surprised it actually hosted some professional international games as the stadium seems small?
They are in the lowest of the English fully-professional leagues. Like most such clubs, they have a complex history, and are regularly saved from going broke by wealthy men who supported them as boys. Their ground has hosted under-16 and women's international matches, but those draw small crowds compared to the adult men's matches. They have good name recognition in London, because of their unusual name, but since the sponsorship is of their training outfits, rather than the kit they wear in competitive matches, its impact will be limited to quite dedicated fans of the side. Those will mostly be locals.
For the avoidance of doubt, this kind of football is soccer, not anything resembling American football. Men's soccer is huge in the UK and Europe; women's soccer is on a smaller scale, more similar to its popularity in the USA. American football is known in the UK, and played as an amateur sport on a fairly small scale, but as far as I know there are no professional sides.
I'd guess that someone at WotC UK had some advertising budget spare, and some combination of personal connection, the dragon logo and a low price led to an experiment.