So let's assume the premise of these proposed observations and let's assume that we actually find a planet with a high pollution content and let's further assume that we're only able to detect the type of pollution that can never be created from some naturally occurring process e.g. don't look at Venus and assume that it was once a beautiful place until acid rain formed. Such a planet will be quite a few light years away, perhaps hundreds. So what we would be looking at is the pollution from a hundred years ago. If this civilized planet is smart enough to fix it, they are more advanced than we are. But we may never know. The EPA was created 44 years ago and many people think this planet is more polluted than ever. We might have to stare at said distant polluted planet for more than 50 years to find out if they fixed it. Then again, if the atmosphere clears up in a year or two, then they either are even more advanced than we are or they destroyed themselves and their planet healed itself. Or maybe the indigenous population actually exists because it's polluted by human standards. Or this whole thing may mean nothing.