That would be false. Possibly all the white racists in Mississippi voted for Goldwater, but in order for Johnson to have landslided he would have had to have won at least 25-30% of the white racist vote nation-wide, and a majority of the non-white racist vote.
So, most of Johnson's votes were from non-racists?
A study (Campell, 1966), notes that about 20% of Southern Democrats voted for Goldwater. Those that voted for LBJ were saying: "Goldwater is right on the Black man, and that is very important. But he is so wrong on everything else I can't bring myself to vote for him." There were no doubt "Racists for Johnson" out there.
Ive also heard of one Black preceint in PA, along the Susquehanna, that voted for Goldwater, which was the only one in the country to do so. It also had a 102% turnout in one election. It sounds like voter fraud.