The original post was updated with more information.

Timnit responded with an email requiring that a number of conditions be met in order for her to continue working at Google, including revealing the identities of every person who Megan and I had spoken to and consulted as part of the review of the paper and the exact feedback. Timnit wrote that if we didn’t meet these demands, she would leave Google and work on an end date. We accept and respect her decision to resign from Google.

I would say that describes a conditional resignation, and the fact that she called this “being fired” indicates she didn’t really plan to resign (ie. she was bluffing).

She called it being fired because Google terminated her employment earlier than she offered to resign.

It’s a strange reaction though. “I’m resigning.” “OK, that’s your prerogative, bye.” “Wait! I didn’t mean NOW! How can you fire me like this?!” Then make a big deal about being fired on social media. Seems to me that someone who genuinely was ready to resign would have just quietly walked away, even if they imagined it ending less abruptly. Can’t know for sure, obviously.

Resigning doesn't mean leaving quietly. Especially for a researcher ordered to retract a paper.