Issues with Former Academic Advisor
Any ideas behind my former advisor's behavior?


Maybe he is a bozo. Maybe he had a bad day. Maybe he misunderstood the situation. What does it matter? You have found a new advisor and moved on with your life. 

I would have just voted to close ("help me guess what he was thinking" questions are off-topic here), but I think there is a real issue in your post, and I think it's this line:


  I asked him when I would be graduating since I was genuinely curious


You should not be "asking" this question! As you've discovered, advisors make mistakes all the time -- it's very common for undergraduate students to stay longer than they expected (and pay extra) because their advisor made a mistake. Instead, you should look up all the classes you need for your major (including gen eds) and make a plan for when you will take each of them. Your advisor (the good one) can help you with this, but any mistakes will hurt you, not your advisor, so it's on you to get this right.

Good luck!