Yeah after finding it on reddit I read some comments and you're right its not just a single atom
"But we really need to clear things up, as people will mistakenly believe that dot is the size of an atom: it's a long exposure picture, which means there's a lot of photons from the atom hitting the camera sensor which in turn activates the pixel that we're seeing as the purple dot. In reality a single atom is much much smaller.
tl;dr: camera sensor pixel =! atom"