Yea this a major difference between St. Patrick's Day and Halloween. Everyone knows St. Patrick's Day is irish but most people outside of Ireland have no idea Halloween is. The other major difference being that the reasons for celebrating St. Patrick's Day are still very true to its roots, but this is certainly not the case for Halloween.
That being said what is interesting about how FFXIV does Halloween is that voidsent are directly involved in the festivities. Many of the voidsent in the game have names of figures from irish celtic legends. So in a way how FFXIV celebrates Halloween is closer to its roots than how people normally celebrate it themselves. I don't know if the in-game connection between voidsent, celtic legends and Halloween was intentional by SE, but I find it cool anyway.
