The court was told he'd believed Mr Paterson had meant him harm.
Hickson told police Mr Paterson had arrived at his Edmonton home on November 6 and had started using tarps and fishing nets to enclose the back yard.
"He (Mr Paterson) was making out like he was making it safe ... to me I was getting caged in," Hickson told police.
On the morning of November 7 Hickson said he and Mr Paterson were both in the lounge area and "we both reached for something at the same time and he was slower than I was I guess".
David Hickson is accused of murdering Campbell Paterson.
Hickson said he grabbed a hunting knife with a serrated blade about 40cm in length in total. "I've just reacted," he told police. "It just happened that quick.
"I just swung it ... got him where I shouldn't have got him."
Hickson indicated to police the knife had struck Mr Paterson in the neck. He said Mr Paterson stumbled and ended up in the bathroom holding his neck.
"I sort of put my hands over his hands," Mr Hickson said.
When asked by the police why he didn't call 000, Mr Hickson said, "Cause I was not in a ... I can't explain why I didn't call 000."