That would an atomic particle of a different color. I did not pick up that it was a single electron. Thanks for pointing that out.
I would still need to know how many electrons were measured at the target site. If a single electron is always received yet an interference pattern exists then it is out of my league. However, two or more electrons hitting the target when only one was sent can be explained depending upon the voltage potentials at the emitter, mask with the slit and the target.
The whole point of the experiment is to show that particles -- electrons/photons/whatever -- form an interference pattern even when fired one at a time. Obviously it takes many particles to form an image of the pattern, but they are fired one at a time. That is what makes it spooky.