There is a customer who buys a lot of music at one time, and there will be a relatively large discount. One of them includes your song. This amount is an additional one after the discount. This is just a special discount for large orders.
It is a normal business practice to sell large orders at a discount, which is also to better sell music.
There have been similar situations before, you can refer to previous posts:https://100audio.com/topic/1781103/