The headline said 1BTC, so I take it to mean "until the price of 1BTC is too high to buy with real money". They're not saying they'll buy $66000 worth of bitcoin per day indefinitely, just 1 whole bitcoin per day, regardless of how the price fluctuates, for as long as that's viable.
El Salvador doesn't have its own currency; they use USD and recently bitcoin. I don't know enough to say whether this makes sense.