lag or server congestion or what?

when i'm playing the game i noticed some peoples characters will run - stop - run - stop while others move normally, am i correct in assumeing this is based on the individuals connection? or is it just server congestion. either way this shouldnt be happening in an mmorpg i have played plenty of mmorpgs with no lag whatsoever except for maybe one indivual in about 500's character doing this due to their own shitty connection. the last time i seen this whole "run-stop-run" thing in a game was on phantasy star universe, which only got worse after they started only hosting the game on servers in japan. like insanely worse, there was disconnecting and lagouts. ffxiv is a fun game and i'm hopeing everything will be sorted out no later than a month after the release, but as a company you got to understand the people dont want to put up with this nonsense. i personally am not experiencing any lag, other than seeing other players lag as they walk/run and some run perfectly. so i assume its based on the individuals connection to the server.

Most likely related to server lag; it's not severe on the server that I am on so I don't notice it too often.