Video footage shows Bishop seated, with a bottle in his hand during pop singer Stan Walker's segment.
Some people in front of him were on their feet dancing and waving tino rangatiratanga, or self-determination, flags.
In a statement to RNZ, Bishop admitted he said something about performative acclaim and said "what a lot of crap". He said it referred to what he called the overtly political branding on display.
"I could hear an enormous amount of ranting, kind of against the whole thing. I didn't get the full gist of it, but it was basically - 'the hīkoi is ages ago, sit down everybody' - so this geezer was just ranting away and telling everybody to sit down," McGlashan said.
"After a while I turned to him and said 'ah, shut up you dickhead' and I looked at him and I thought, 'oh, I know that face'. Then he said, 'What did you say to me?'".
McGlashan said that he again told Bishop to "'shut up you dickhead', and he said, 'I could say the same to you,' and I said, ,Well, I wasn't talking and you were.' And then I realised I was talking to the leader of the House".
"For him to take an instant dis-gratification towards Toitū Te Tiriti and that movement and to say that it's a load of crap is actually highly offensive. I'm very worried for somebody of high power in this country to be making those sorts of remarks in public," they said.
In a statement to RNZ, Bishop said that, on reflection, he should have kept his thoughts to himself.
A spokesperson said he strongly denied any other allegations - including making comments about the hīkoi - and said it was a political smear job: "Chris is a long-time supporter of New Zealand music and went to the Awards to celebrate successful Kiwi artists."
