I'm actually super impressed they found and fixed a deadlock that quickly. Deadlocks can be notoriously difficult to track down and fix.
For those curious, a deadlock is when two threads, or streams of work, in a piece of software attempt to acquire a lock to a resource (generally a network resource, a database table, chunk of memory, etc). but due to a bug they both sit in the "waiting to lock" state, while the lock is never released. The threads then "deadlock", effectively going to sleep forever waiting for a lock that never releases. They are a notoriously difficult class of bug to debug and fix and are one of the main "There be dragons here" issues in multi-threaded programming.