As a professional in the industry, seeing celebrities is pretty common. It's really good to be lowkey and have a small chat to break the ice when bumping into one. Celebs tend to be more energetic and interact when they're ahead of their day. Most celebs will already be burnt when you spot them from all the marketing events and photoshoots so you can tell by their body language that they're not in the mood for small talk. It never hurts to try to talk to one just as long as their not hinting their drained from all the crazy functions they've been juggling.