It's unrelated, except for the fact that I used the reverse engineering of the facebook messenger protocol by the mautrix team [1]. XMPP has had bridges more or less from the start. [3]
I may add a "matrix plugin" [2] if I feel like it someday, but probably after I implement group chat support. Then you'll be able to use XMPP<->Matrix<->some-other-thing for extra over-engineering points. ;)
I prefer XMPP because it's lighter on resources, server-wise at least, and it's managed through a democratic process, which has it upsides and downsides. As someone I like said "democracy is boring, dictatorship works faster".
[1] https://github.com/mautrix/facebook