That implies that significantly less than half of their income fell into the highest bracket. This is true of the top 0.01% as well (the top 1% of the top 1%), they paid about 50% overall.

So, the top 1% of the top 1% of high-income earners, found a way for their income that would fall into the top tax bracket, to not be income. They turned it into capital gains or something else. To not do so would be crazy, so literally no one let a significant amount of their income fall into the top tax bracket, in the 1950s.

The difference between 42% (1954) and 36% (2016) is massive, and we lowered their taxes even more since then!