While you are correct on knowing the location of the factory switch on the Model 18 (on the side), there are aftermarket switches/levers available that replace the back plate of the slide. These replacement back plates are evidenced in the pictures provided in my previous post. If you look at the picture in the original post, you will see that it appears too small to be a Model 18. This means it was probably fitted with an aftermarket select fire switch/lever, and would be located on the rear of the slide and not the side.
You're absolutely correct.
Glock Fullauto conversion - RH-Custom