If you're just walking by my house can I beat you up and claim I was just protecting my house? OP clearly stated he was keeping his distance when it attacked.
Did you even read
Maybe it had babies and you were near them?
I mean, a parent and it's babies
are separate physical entities. It's perfectly reasonable to suggest that he may have stumbled too close to some small, hidden babies without being near the parent.
Also, animals aren't capable of rational thought as much as humans. 4.5meters is quite to close for comfort for most animals