Unless a group of humanoid aliens monitoring Earth crash landed about 2 million years ago with no hope for rebuilding their ship. After the survivors discovered that they could breathe the air, they decided to bang some homo erectus for fun (and because they could not shake the attraction of their musk). Strangely enough, these humanoid aliens were able to interbreed with homo erectus thus leading to the evolution of homo sapiens. The humanoid aliens taught the homo erectus their language and passed on pieces of their knowledge.An alien would likely share little or nothing in common with us. There is no common ground around which languages can be translated to one another. You might be able to communicate plain facts, like Earth is the third planet, but nothing abstract or meaningful.
Just playing devil's advocate here. I agree with your assumptions generally, but, there's could always be a different answer. But we won't know for sure until we know. We may never know.
Unless Babe Ruth was an alien....I simply am not so naive to think I can buy a CB radio and talk about baseball with aliens.