A friend gave me this orchid two days ago. It is almost certainly a species, taken from the trees in the state of Minas Gerais, Brazil. The climate would be warm, nothing lower than 50 degrees F. Wet overcast summer, dry winters.
I'm pretty sure it's an oncidium, since it's very similar, and my other oncidiums are in bloom now.
You're very right. It looks just like the Miltonia regnellii on this site: IOSPE PHOTOS
I was really glad to get some hints about what it likes, and especially to know not to worry about the yellow leaves.