I wonder how much he might be regretting signing himself up to this. What you'll tend to find is these politicians usually lack much knowledge about what they're preaching but are keen to use any hyped up new trends to their political advantage. Cryptocurrency is still seen as a modern and innovative concept (it is, barring the environmental issues to be solved). Coinbase is probably bumping up his salary behind the scenes as this is indirectly favorable advertising to them, he might slide into a comfy "consulting" type job working in this company after he leaves office. This definitely sounds like a carefully engineered story, because as you posted - he got paid in USD and made a choice to convert it after that point.
he knows a bit more then you think. he is already looking into repealing the NY bitlicence. so he knows about the laws hindering bitcoin innovation in NYC
he also know about the mining side of things.
im not fan waving his salary announcement. thats just side drama stuff and not as important as the 'NY becoming bitcoin innovation centre' announcement.
but those saying he might regret it, as if he has no other income or savings. pfft. the guy is not poor. he has $2-$3m net worth
so $21k a month for 3 months is not that much to miss.
i am a little bit more critical about his republican aspects and that he wrote a book about herbal medicine (which gives me a few doubts about his decision making)