What's more it appears to be incredibly terrible math.
The seekingalpha article says the assumptions are 1.7 million "new" subscribers to Youtube TV (plus NFLST) and a half million NFLST only subscribers.
If you do the math 1.7 million subscribers to Youtube TV at $65/month is $1.326 billion, and 2.25 million subscribers to NFLST at $300/year is $675 million.
OK, that adds up to $2.001 billion so $1 million a year in profit after paying the NFL $2 billion, right? Only if you assume Google has zero cost not only for delivering NFLST, but for delivering Youtube TV! And they obviously don't for the latter after paying $10 for ESPN and $25 for local channels, not to mention the rest. They probably don't even make a profit at $65/month but even if they do it is only a few dollars a month not $65 a month!
Now obviously Youtube is banking on individually targeted advertising to create revenue, using the 2 to 4 minutes per hour reserved for local affiliates (for NFLST and other network broadcasts) or commercial insertion slots for "cable TV" channels like ESPN or HGTV. How much they make from that is the unknown, but that's obviously where they hope to monetize NFLST (especially if they can get people to "cord cut" from cable/satellite and sign up for their virtual cord)