Pick any one of the following:
- Aircraft in front slow to clear the runway.
- Landing clearance not received in time.
- Excessive float (for whatever reason, probably wind).
- Anything either pilot was unhappy with.
Very unlikely to have been too fast - if they were, they'd have gone around much earlier. You cannot judge an aircraft's speed from the sidelines, or even by looking out of the window - that's why we have airspeed indicators!