Though the shock delivered may not cause physical damage, it does cause pain and there can be mental consequences.
In my car, I use plastic Vari-Kennel crates, for whatever reason they began building a static charge and would zap my dogs when getting in or out. I did realize right away what was going but my boy's reaction very dramatic. He would cringe and act as if he was going to be hit when asked to get in the car. I now make sure that the crates are all well sprayed with static spray periodically. Though my boy was not physcially damaged, it most definitely had a negative impact on him.
It is important to be aware of how these devices work and watch closely for signs that it is effecting the mental health of the animal not just to worry about physical consequences.
But you were trying to make him jump into the thing that was uncomfortable to him. I mean, if I were trying to make Keoki stand on the mat, I'm sure it would do some psychological damage.
But, having been startled by it the one time, he simply avoids the mat; we encourage him to avoid that area, so there's no mental health issue, IMO.