What does a Lockdown implies?
There generally aren't a lot of status meetings, team meetings, project meetings, and so forth at Facebook, but you might want to turn down a request to present at another team's meeting, or turn down those requests to interview - they can wait, or another person can be found.
People tend to make progress on lower-priority work items in between higher-priority work items - things like migrating onto a new library or version of a service, or maybe migrating from one set of machines to another if you aren't using one of the high-level service management systems. This is necessary to prevent these things from becoming interrupt items down the line, but during a lockdown period, it's okay to let these slide for a bit.
If the whole team does this, then suddenly you're spending a lot more time together. Instead of potentially working on different parts of the software like you usually do, you can all focus on a particular class of problem - in this case, performance and parity. That means everyone has that context loaded up, and you can have better discussions and quicker code reviews.