Those people also had melee cavalry which were good and had perhaps even taller horses, but then the question comes how the knight defeated them on equal terms or even when outnumbered, it wasn't as if they were equipped that much better (and apparently worse in regards to horses).
Massed lance charge. It took some time before anyone else's heavy cavalry (or for that matter, infantry) became used to that, and until then it gave the "Franks" a pretty serious advantage in the initial collision. Even after they became used to it, trying to avoid overmuch exposure to that terrible shock impact tended to be among the chief tactical concerns of anyone facing them. Skirmishing horse-archers usually made a pretty good screen if deployed correctly, but not everyone had access to the prequisite horse herds (the Mongols famously considered 18 mounts per trooper a good number to start a campaign with...); "civilized" HAs - say, Byzantine, Russian or Mamluk - for example could not indulge in such mount-tiring tactics.

It's not like cavalry hadn't near-universally known the basic trick behind the couched charge since God knows when, but the European heavies came to specialize in the technique to a fairly unrivaled degree. They still occasionally lost even straight head-on clashes where they could employ it to the full effect, though. So it goes.

I've incidentally also read that one reason feudal cavalry never became as important in most of Scandinavia as in rest of Europe was bluntly that the local horse stock was rather ill-suited for heavy cavalry duties, and hence the men-at-arms had to mainly rely on imports (which jacked the already high price up even more, and most of the region wasn't exactly prosperous...). And when the Swedish entered the Thirty Years' War, one of the things they did ASAP was to swap their native horses to rather more battleworthy German breeds; the same would apparently happen later on in the Polish adventure of Carolus X.