It's just harmless client-side modding to replace everything with Thancred.

However, the fact that player movement is handled 100% clientside makes XIV extremely susceptible to some forms of hacking that are genuinely harmful for gameplay balance. I've seen multiple players using speed hacks that effectively give them infinite sprint speed, PvPers making themselves immune to bind/snare effects, and of course the obligatory teleporting gil farmers in ARR areas, but only the latter of the three actually seem to get punished with any degree of frequency.