GW2 is popular and recent and it's pretty obvious where SE drew their "inspiration" for it.
I'm not so sure about that, remember this game has been in development for 3 years and GW2 was released only a year ago.

I mean if we're getting really picky, open world events were in XI too (e.g. Campaign battles). The only real difference with fates is they don't occur at an outpost and there's slightly more variety. The positions are still fixed though, just like campaign.