I also think it is defined by the airlines seperately. But probably it also has something to do with the crew-contracts.
At KLM the Long-SHort definitions are defined as Intercontinental ICA and Europe, and these groupings define what aircraft training the crew gets.
SNBA sends its A319 up and down to TLV
in one go, so it could also be defined as shorthaul.
But surely there must be something like medium-haul, or is this just used to define aicraft range?