Just treat the officer with respect and courtesy. Their job is difficult enough as it is.
That. I worked with police officers at my job for a while and their job sucks. It's really harder than most people know. However, I am talking about our City police. I will refrain from commenting on the police from our outlier burbs around here.
That said, you have to have a little boredom in your life to stop someone for vaping. Every day I make eye contact with at least one police officer while vaping in the car because where I live I literally share the parking garage with a police station. And I had no issue so far.
The problem of probable cause is very debatable here. If they are simply asking and then they act like this one in this story, that's fine. They can (and should) include any strange / unusual or inappropriate behavior in their judgement call. If they go any further in absence of anything suspicious, they are in the wrong, because then they should stop and check every person smoking a cigarette (cigarette like objects are the most commonly used illicit substance delivery method), drinking any sort of liquid, and even eating. Simple as that.