The person kept saying that what they did was "just like jaywalking," but as soon as they were called in by HR they knew they were in serious trouble. That doesn't add up.
Perhaps speeding would be a better analogy. Everyone does it, but when you see the blue lights(or get a meeting req with HR) you know you're in trouble.
It doesn't sound like the violation and the investigation were temporally linked though. When you're speeding and you see flashing lights, you know you're in trouble for the thing you're doing right then. If some minor violation is common practice (everyone is doing it all the time), how would you know immediately that you were in trouble for it when you get the meeting notice? The person even said that they had previously been called into HR as a witness in investigations of other people, yet this time they knew they were being investigated without being told.
How about a red light camera? Pretty commonplace to push a yellow light, and when you get the envelope in the mail from the city ticketing office you probably know what it's about.