When he appeared before a congressional committee he was asked directly "Are you stupid?" He politely apologized for his comments but is there really any doubt that he meant it at the time. He was recorded on several occasions saying it. Was he referring to his perceived stupidity of the Tea Party voter or the Single Payer voter? Maybe both. Gruber did work with Mitt Romney when he was governor of Massachusetts
I have cited many surveys which indicate the both the Tea Party voter and the rest of the electorate are not as stupid as Gruber believes. The polls have consistently suggested that the individual mandate was the least popular part of the ACA. The other provisions, expanding Medicaid, banning the denial of coverage for preexisting conditions and subsidies for low incomes to buy insurance are popular among all Democrats, Independents and Republican voters. Pretty consistently, if one adds those who support a better bill (i.e. Single Payer) to those who support the ACA, one has a majority.
Of course Republicans are not above relying on the perceived stupidity of the voter to get things passed too such as pushing the imaginary Iraq-Al Qaeda-9/11 connection to the US public to sell a disastrous invasion in 2003.