I think the disconnect is that you're thinking of the "market price" as being something that exists on its own. It doesn't exist, it's entirely a function of the trades that happen between buyers and sellers.
The reason people say "selling drops the price" is because when there is more sell pressure (lots of people wanting to unload an asset), it becomes harder to find takers. They need to improve their offer (i.e. lower the price they are willing to sell at) in order to find willing buyers. So the exchange rate of subsequent transactions drop. Then when you measure the average exchange rate of the latest transactions, you get your "lowered market price".
I think the disconnect is that you're thinking of the "market price" as being something that exists on its own. It doesn't exist, it's entirely a function of the trades that happen between buyers and sellers.
The reason people say "selling drops the price" is because when there is more sell pressure (lots of people wanting to unload an asset), it becomes harder to find takers. They need to improve their offer (i.e. lower the price they are willing to sell at) in order to find willing buyers. So the exchange rate of subsequent transactions drop. Then when you measure the average exchange rate of the latest transactions, you get your "lowered market price".