all aircraft have to carry additional fuel to meet legal requirements with regards to diversions and/or holds.

It might have been the case that the expected hold time was going to be too long so the aircraft was diverted.

Happened to me a couple weeks ago on AA where we diverted to STL because it became obvious the storm wasn't going to move quickly enough to allow us to land at the original airport.

however- if there is a pattern of strong headwinds (for example at a particular time of year) - you would expect the airline to load additional fuel to cope with this.