Zoom is a US Based, publicly traded company listed on the NASDAQ [1]. So to that first part, no, that's not correct.
However they have a Chinese subsidiary that does some of their development work along with supporting their in-China services. Any tech company that operates inside of China is legally obligated to private the CCP access to anything and everything they want. This is why most companies has separate, special, dedicated servers for/in China (up to and including AWS [2]).
The reason for the purchase of Keybase is to up Zoom's crypto game. They (Zoom) made a pledge to do significantly better around encryption and user controls, right after they became super popular and started getting targeted for news/abuse/etc.
Sadly it probably doesn't matter what you think of Keybase as this looks like this was probably an Acquihire for the team and their knowledge. Maybe Keybase the product will be totally open sourced, but beyond that it's likely dead.
