The odds of convergent or parallel evolution are essentially nil, even if the other planet was exactly like Earth, there are just too many events on Earth that would not have happened on the other planet and vice versa that shaped our evolution. Think butterfly effect. Only real conclusion would be that a third alien civilization transplanted some of our humans onto an Earthlike planet. The big question is why. Secondarily, how may other planets have humans on them? Are the aliens still around?
In that case, our primary interest would be to find out more about that civilization. Yes, humans are inherently violent and competitive, but we would not go to war with them unless the others attacked us first. Yes, our religions would try to convert them, and vice versa. Science would likely benefit assuming they are at or more advanced than us. Certainly, they would know some things we don’t. Most likely we would bond with them, study each other’s culture and history, etc., especially we would want to know more about those aliens. They would be curious about our natural evolution and history as the home world they came from.
Remember, humans only fight each other in the absence of a third party mutual enemy. Although the aliens would not necessarily be the “enemy” they would be our mutual primary interest, being superior technologically. Some would fear them and worry about being judged by them. Others would covet their technology and seek to obtain it. Others would seek their wisdom and guidance. Both worlds would work together to seek them out.