According to Taylor's monograph it is a terrestrial, although I have seen people refer to it as an epiphyte as well. The only photos that I have seen of it in the wild have been growing on the ground. At this point your plant is either dead or established, so my experience likely isn't particularly useful to you. But, for others, I have had success growing it in a standard peat/sand mix with a high water table.
It seems that some people assume that all of the plants in section Orchidioides are epiphytes. And, I wouldn't be surprised if people assumed that longifolia is in that section because of the large flowers and range. But no, it is section Foliosa. I'm not sure where the misinformation is coming from, but I'd wager a guess that it's related to this.