I don't believe this is true.
Us Code Title 3 Chapter 1 is clear that there is a difference between "appointed" and "apportioned."
The the 538 votes are "apportioned" to the states, but the winners on Election Day are "appointed."
Both the Constitution and Title 3 are clear that the candidate needs a majority of "appointed" electors, or in other words, a majority of Electoral College votes cast.
-PJ
“I don’t believe this is true.”
Looking at the elections of 1864 and 1868 when Congress rejected the electors of some states, the benchmark needed to win a majority did not decrease. It remained the same. At least that’s how I understand it. In 1864, a candidate needed to win 117 EC votes out of a total of 233. Lincoln won 229 but 17 of them were invalidated by Congress which still left him well above the 117 EC vote needed.