Earlier quoted context omitted.
I don't know the specifics, but the license included with that code will specify what can and can't be done with it. ~~Not all open source is free to use in your own code base. Sometimes it is open sourced for review purposes.~~ Edited: the last line is incorrect.
> Sometimes it is open sourced for review purposes. Huh? I'm not aware that it's possible to open source something without, you know, making it OSS. Am I mistaken, or are we talking about two different meanings for "open source"?
The agreements for opening code up for review purposes only is indeed not OSS, despite the word 'open' often being used there.
I started off sound, then diverged. The part of Twitter that was open sourced will have a license spelling out what you need to do (if anything) in order to use the code. The review part is a different thing.