How much of that is revenue from actual crypto-related business vs. just appreciation of crypto the company owns? Feels like the impressiveness of this trend really depends on that

Their Bitcoin "revenue" is simply the face value of the Bitcoin they sell.

It's like if Charles Schwab counted any stocks people bought as revenue.

I suspect the difference is that SQ may hold the Bitcoin and sell directly to the user rather than as a broker. But calling it "revenue" is still highly misleading, as margins will be razor thin, by definition (the transaction fee)