"No, because someone signs a referendum doesn't mean they're necessarily going to vote opposed to it," he told TV3`s Firstline.
"Over a million people voted in the last election for National when the then Labour leader said this election is a referendum on asset sales."
Key said the people who signed the petition were absolutely entitled to be heard.
But the referendum asked whether people supported asset sales - not whether they wanted the programme to be stopped.
"That's a different question, actually, some people might accept."
Green Party co-leader Russel Norman told Radio New Zealand the majority of people at the last election voted for parties opposed to asset sales.
He said taking account of votes for the Conservative Party, which opposed asset sales but did not pass the threshold to get into Parliament, 51 per cent of electors voted for parties against the sales.
Norman said voting for Key or National did not mean someone supported asset sales.
"Most people didn't. On top of that again we've got a citizens-initiated referendum underway right now.
"I would say to the Government, suspend the asset sale programme so we can hold the referendum at the same time as the next general election, and then we can specifically test, do New Zealanders want to go ahead with privatisation of these key energy assets, or do they want to keep them in public ownership?"
Norman said the Government was being "incredibly arrogant" and Key was saying the people who signed the petition for a referendum did not count.
The Government has until early next month to declare a date for the referendum.