I thought his behaviour seems territorial too.
But thing is, It is a new room for them.
I moved into his house and not the other way around so it is a totally new place for them. It seems fine for the first few months though. But not anymore. The last time I had him give the boy treats, he's still attacking after that.
He jumped and bit his finger hard until it almost bled.
Hub's getting frustrated and impatient.. So now, I'm doing the treats and if he bites, back to the cage. Sigh.. I hope this improves soon or he'll be short of freedom time as I can imagine having to choose either one in the room and not both at the same time. :(