This is a little absurd:
I don't agree. Humans have killed humans for a long time, but in sheer numbers of deaths and the recreational way in which it was done, fifty million intentional deaths is no trivial matter. Remember that the same rate of killing was going on in the Northern herd at the same time.
I'm not weighing human life against bison life; simply life to life. Many people have been killed as collateral damage, but if you ranked intentional genocides by time and volume, the bison would top the list.
We were taught the same, clinical fact in History also, but it was just that simple fact; glossed over as step 1,2,3 in making the West habitable for settlers. The pesky Indians kept killing the settlers and the buffalo is about all we were left with from the educational process. Not your fault and not my fault...or the teachers' either, I suppose. Just a fact from history.
"I'm not weighing human life against bison life; simply life to life."
You are contradicting yourself. You are comparing humans and bison as if they are equal in some way. Killing even one human is worse than killing any number of bison. But lets consider it on your terms, bison would still not top the list.
In that case it would be easy to argue that the extermination of the passenger pigeon was a far greater crime for two reasons: first we hunted them all the way to extinction and if the number of lives matters for some reason then secondly we killed somewhere around 5 billion of them, 100 times as many as bison.
Do you have any verifiable proof of that, or is it only because you are a member of the dominant species and that is the viewpoint of your species?
I agree that the Passenger pigeon should be first on the list, just above the bison.
your article noted that the bison didn't care when their families were shot down. People do.
This might help you make your list:
https://www.thoughtco.com/recently-extinct-animals-1092157
and there is this:
"According to the research, published today (Jan. 29) in the journal Nature Communications, cats kill between 1.4 billion and 3.7 billion birds and between 6.9 billion and 20.7 billion small mammals, such as meadow voles and chipmunks."
https://www.livescience.com/26670-cats-kill-billions-animals.html