Yes, whatever portion made their decision based on cost of groceries do believe the president influences prices. It’s the same as the old line about “gas prices are too damn high”. Most people aren’t very involved in politics and they don’t understand things like this, or that economic cycles are so long that half the time it’s the result of the previous party’s actions what is happening now.
Harris played to and reinforced this economic illiteracy by proposing federal price controls for groceries.
But I mean what else could she do? You tell the electorate the truth and they don't understand it or don't listen, you lie and say "fine we will fix it with price controls" and they freak out all the same. Only one side of the political apparatus can like with impunity, apparently.