The Sweden striker returned to St James' Park for the first time since his £125 million move to Liverpool, facing sustained boos from Newcastle supporters before and during the match.
Liverpool eventually drew 1-1 after Dominik Szoboszlai converted the late penalty, with Isak not taking responsibility for the spot-kick.
Alan Shearer questioned the decision on The Rest is Football, asking why Isak had not taken the penalty himself.
Isak addressed the issue while on international duty with Sweden.
“Szoboszlai was the penalty taker for that match.
“It’s a bit irrelevant (Shearer's verdict). Those are team matters, and it’s not for the media or the supporters to decide who should take a penalty. I’m always hungry.”
The forward also described the reception he received from his former supporters as an unusual experience, although he had expected the atmosphere before arriving.
“It was special. I was prepared for the atmosphere, so it was a special match.”
Isak's departure from Newcastle followed a turbulent summer in which he pushed for a move before eventually joining Liverpool for a British-record £125 million. Contemporary reporting confirmed the hostile reaction from Newcastle supporters during his first return.
His first season at Anfield was then disrupted by fitness problems and a broken leg suffered in a match at Tottenham, leaving him with a lengthy spell on the sidelines.
The striker returned in time to be part of Sweden's World Cup plans and has begun the current campaign in better physical condition.
Asked whether he viewed the new season as an opportunity to make up for his difficult first year at Liverpool, Isak rejected the idea that he needed redemption.
“I’ve been focused on having a good season, considering last year.
“It’s not about redemption, but about having normal ambitions to do well. I’ve had a good start, but it’s still very early. I shouldn’t talk too much about it.”
He later reiterated the same point.
“It's not about making amends, but having the usual ambitions to do well. Compared to last year, I feel like I'm in a much better place now, physically and everything.”
Isak has already scored four times this season, including the winner against Bournemouth in Liverpool's final match before the international break. Reuters confirmed that goal secured a 1-0 victory for Liverpool on September 20.
The Sweden international is now looking to build on that start after a difficult opening campaign at Anfield, with his return to Newcastle having provided one of the most charged moments of his early Liverpool career.