In fact, just looked up these results by CNN: https://www.cnn.com/election/2020/results/president
So Biden is reported as receiving 51.3% of the votes which is reported as exactly 81,284,666 votes. Though clearly if you sum all the votes and calculate Biden's share, you would not get exactly 51.3% but some other number, perhaps 51.31112341% (couldn't do the actual math as the page only reports Biden and Trump's votes but I believe there were other very small candidates who must have received some small number of votes). And if you took exactly 51.3% of all votes you would not get 81,284,666 but some other number close to that.
So I don't follow what's suspicious here? (As to whether there was election fraud or not, that's a completely different question, not commenting on that here.)
Update: Never mind the above, I had in my haste misread/misunderstood the point of the article :/ (see reply below)