No this is not rare at all. Meta offers E5 ("senior" level) new hires a 400-500k total package in the US (given that you negotiate, I know the levels.fyi numbers are a bit lower), and this isn't some exception. If your performance is good and/or stock appreciation happens, then that number goes even higher.
I'm a very average engineer (probably way below average amongst the HN crowd) and I'm in that range.