Q: "A long-haired guy doing a backflip on the trampoline." Does this mean that "There is something to jump on."?
A: yes

Q: "A band of musicians performing for a rally." Does this mean that "A band is rehearsing in an empty rehearsal hall."?
A: no

Q: "A man is selling a huge variety of blown up balloons outside." Does this mean that "The man is in bed asleep."?
A: no

Q: "Little boys in white karate uniforms performing their martial arts indoors." Does this mean that "A group of little boys are participating in a martial arts tournament indoors."?
A:
it is not possible to tell