Is it really rude and bad behavior to assume in American custom?

I'm Asian and my boyfriend is American. He often gets really mad at me because of my 'assuming' as he calls it. But I don't understand him fully. Like for example when I said, " I thought you left your house because no one receives the package that I sent you." He was so mad already and said that's assuming. He said he was just at the house all the time and was in the kitchen but not just able to answer the door immediately. I admit I'm just guessing and thought he just went somewhere to his friend's house but what I don't understand is why is he so mad. I told him it's just a small matter and he didn't need to act that way and again his temper got far more worse because I said it's just a small problem. Whenever he gets angry he uses abusive language to me and call me names. Another is when instead of messaging him on facebook I texted him on his phone. He got really annoyed when I asked for the 2nd time what is he doing. I was waiting for him on facebook and posted a video for him to watch but he's not talking there because he's playing farmville so I just thought it's much better to text him instead to get his attention but he got very irritated. Is it really rude in America to assume? He often said that maybe it's okay in my country but not in America.

You need a new man. Plain and simple. Nothing to do with you. He sounds like an ass. Google Simon and Garfunkel's 50 ways to leave your lover.

Yes, sounds like he has a problem with himself, not you. Interesting to see that the "keywords" suggested under your post include - anger management, bipolar, mood problem, attitude . . .
Try to work something out so that you can move on without getting hurt.

In case you were still on the fence...that is irrational and uncalled for behavior. As an adult you need to bring it up to him and decide if you two are willing to work through it to make you both happy.