F4/A4 means they're willing to sell 4 seats in A booking class and 4 in F booking class. The numbers don't add up to a total — if they sell 1 F seat, it'll go down to F3/A3.
Given that all LH planes (with F) have 8 F seats, F4/A4 means that half of the seats are sold (or excluded for sale for any reason).