> Wasn’t the tweet recommendation system “open sourced” as well? Does this guy know the difference between open source and “open source”?

What do you mean? There exists only one binding definition of open source

> https://opensource.org/osd

and either some product does satisfy it, or it doesn't. As far as I am aware

> https://github.com/twitter/the-algorithm

does satisfy the open source definition, so your sarcasm looks demagogical to me, but I am very willing to learn something new.