When you're dealing with particle physics, unless I'm mistaken, the term "experimentally observed" means "non-wild" or "controlled environment observation" and is interchangeable with "observed" as in non-particle physics.

Humans can't physically observe subatomic particles, nor can we (at current) capture real-time video or anything of them. We observe the measurements and math from designed and run experientns, and present the finding we make on those events. I'm not sure we'll have any kind of technology to catch an observation in the wild in our lifetimes.