If it's for two or more tickets, likely the price was for one ticket (there was just one seat available at the price) and the pricing system is set to display the lowest price, regardless of the seat # requested. That is, for multiple seats it doesn't automatically go to the next higher fare class with the # of seats requested.
It's always a good idea to book multiple seats one-by one. Vs. paying the higher fare class price for two seats, getting it as two separate PNRs can get one at the lowest fare class (last seat avail), while only pay more for the second seat.
I always, before booking any multiple seats PNR together, I price it out separately one-by-one and ensure that the price of booking it together doesn't fall into a hire fare class vs. doing it one-by-one (at least for the first seat).