Perhaps a Tolumnia or a Rodrumnia or a Zelemnia or ?

My money is on an Equitant Oncidium......(and that may be what Arthurm is saying, since I am not familiar with either of the three species he mentions). They like growing on small twigs, but a small pot like yours is fine. They seem to be sensitive to some chemicals found in some city water supplies. Would recommend distilled or rain water...(but these days you never know what the Chinese are putting in our rain water)...They like even a bit more sunlight and warmth then Cattleyas, so probably an east window with sun up until around noon, or put them outside in light shade. Tiny little flowers on long spikes for the size of the plant....I think they are real knockouts in bloom. little or no fragrance.

Bill