Should a lesson horse spook?

My dad owns a horse stable, and now that I'm seeing him..I get to have lessons. I ride a 9 year old gelding. I've only had 2 lessons, and on my second lesson..the horse spooked and took off. When someone shut the dumpster lid, it made a loud noise. The horse kept trying to run around and play with his paddock buddy that was also in the arena. I found it hard to keep control. The owner of the horse(my dad's gf), got on him and said that it wasn't me..it was the horse. When I asked what horse I'll be riding next time, my dad said the same horse. Do lesson horses sometimes spook? He was totally fine my first lesson, and my dad said it was because he was exercised beforehand. He also told me that they will tire him out before my next lesson.