As an amateur musician for the last 40 years, I can confirm that this is, in fact, a trombone. Since I am not a trombonist, I can't tell much else about it, except that it clearly does not have the F-attachment.
It's an extra loop of tubing inside the part that goes over your shoulder, operated by a thumb trigger. It effectively lengthens the air path, lowering the tone produced. I only know because my brother played one. He was actually pretty good at it.