The first refers to a time in the immediate past. It has just happened. The second refers to something that is happening right now. Suppose Jim and Mary are shopping in a mall. Mary: Why is that old man approaching us? Jim: I don't know. Old man: Paul and Lucy! What a pleasure to see you again after all these years! Jim: I'm sorry, sir. My name isn't Paul and I don't remember you. Old man: Oh, I'm so sorry. Please forgive me. [Walks away] Jim: The old man seems to have mistaken us for some people he knew years ago. The moment is over. The man has left. Mary: Why is that old man approaching us? Jim: I don't know. Old man: Paul and Lucy! What a pleasure to see you again after all these years! Jim: I'm sorry, sir. My name isn't Paul and I don't remember you. Old man: But I know you! You were in my math class at Wilson High School. Jim: [To the man] I'm very sorry, sir, but we aren't that couple. [To Mary]: The old man seems to mistake us for some people he knew years ago. Old man: I can't be wrong! I remember it as if it were yesterday... The moment is not over. The old man is still there. In the second situation, Jim might also say "The old man seems to be mistaking us for some people he knew years ago."

"Having confused us refers to the fact that he was confused." and "to confuse us refers to the fact that we confuse ourselves."