If 50 out of 5.5 billion were odds to win the mega jackpot lottery, sure. The chances seem insignificant and super low.
The problem is, 5.5 billion numbers are being rolled every day and 50 people out of a much smaller selection pool are going to win. So, if X has a total of 2000 advertisers that give a shit about ad placement, someone has a high chance of winning. Multiple times.
The actual odds are based off of the total number of advertisers and are only loosely based on total ad impressions. Here is what I mean: Every tweet, antisemitic or not, will be close to an ad and not all advertisers care where their ads land. If you find a Nazi, you will find an ad.
You can start doing the math about the actual distance a tweet is from an ad and stuff. Whatever.
This is the important bit: 50 out of 5.5 billion was just what Media Matters showcased and absolutely does not show the entire problem. It’s much worse.