> What type of algorithm would ignore this traffic

Here's are some algorithms that would cause behavior different than what you would expect:

* Take rate of tweets into account

* Take the geography of tweeters into account

* Only allow a topic to trend if it has an odd number of letters

Obviously the real algorithm probably doesn't count the letters in the topic but it could be if it was a bug. It appears your mental model for how something gets into trending topics is:

* Take the topics that have the highest total tweets per day.

That is almost certainly not correct.

> This has some human fingerprints.

You absolutely don't know that. It's pure speculation.