Probably. If it says 4 are left and I try to book 5, it will increase the price and fare class for all 5 passengers.

That said, I used to mimic this with mock bookings for X passengers to see how many were left in that fare bucket. Just yesterday, a certain flight over a month away had at least 9 seats available in L as it has had for the last several weeks. This morning, it only had 2 available in L. Yes, it's completely possible that 7+ were purchased overnight, but that doesn't stop me from scratching my head a little.