A sonic boom, on a small scale, isn't something impressive...bullets cause sonic booms, even the tip of a bullwhip will. I had been around high explosives before too, an oddity of my father's profession. This wasn't just a loud jet, it literally sounded like a bomb, and it resonated for what felt like 5-10 seconds.
But, the cone of condensation coming off the body of a plane is the supersonic shock wave.
And shock surfaces can be present over the body due to local flow speed being supersonic even when the aircraft's velocity vector is strictly subsonic. Though to be fair, still in the transonic realm if you're seeing shocks.