That explains how they chose to minimize deadlocks.
Yes, if you use it incorrectly and/or for the wrong problem space, you will have issues. It isn't a magical solution to all problems. It is, however, an effective solution for a specific problem space.
I've been using it in our development environment. It locks like crazy.
This is after configuring HAProxy to have a primary node which all connections go to.
OpenStack seems to be OK with it though, it chugs along without fully breaking down. I'm sure I would see a pretty big performance delta if I ran a benchmark against it with and without Galera.
That is more likely what they'd have in mind than a single MySQL master container.