>The only way to see such a particle would be to hit it precisely with an even smaller particle and get it to bounce back.

Bounce back from what force? Whatever forces would make it interact with a single particle would make it interact with a detector, which is itself made out of particles.

They say the extra-stable tetraquark would only be susceptible to decay via the weak force, which means you'd have to wait around until it decayed, and then you'd often be able to see some charged remnants.