Yeah, I bet anything this is a caching issue. I assume there's a part of the page which one layer of templates expects to be cacheable, and then someone added this dynamic promotional upgrade feature inside of it, so it keeps being stored into the cache with random people's details in it, whoever was there each time there was a cache miss.

If this is some content that isn't always shown, it could be semi-rare for the upgrade message to show up at all, which is how this kind of thing sneaks past basic QA. Also sometimes QA is operating with low traffic, such that you might still just see your own information simply because you're the only one using the site right now.