For me, it's a little tug, just to get their attention. Usually it's combined with and "Ahht" or something like that.. I use it when my dogs get too far ahead of me for my liking.
As far as being a positive trainer and using a leash pop, I think it's probably the lack of regulation and inconsistent usage. One could argue that a leash pop is "positive" since it's IS positive punishment. Obviously that's not what the vast majority of people mean when they say positive trainer. But if you have someone hung up on a technicality, it's possible.
I'm a "balanced" trainer myself (more ambiguous terminology lol). I use a lot of shaping, I use the clicker a lot, but I'm not above a "NO." or a leash pop.
Watching someone train is definitely much more valuable to know their methods than reading their description of how they train. I would ask about it, and if the trainer doesn't suit you, look elsewhere.