Click a buy button and look in the payment box and above. Above the payment amount will it show the actual minimum price. Any amount shown in the box is a suggestion.
Your first screenshot shows, the project is free to download. The second screenshot ... shows the project page. Click it's buy button and you will see the suggestion is $ 5.00 and the actual price is 4.99. You can enter any price that is more or equal to the minimum price. Any amount over the minimum price is overpayment. It is the pay what you want thing.
These suggestions obviously are not modified by a discount. They're suggestions after all. Only the actual minimum price shown above does matter. You could have entered 2.49 in the box, while the project was on discount, even if the box still shows the undiscounted $ 5.00 suggestion.
It gets complicated, because the actual file on that free project is an indiviual priced file, so paying 0 will not give access to the file.
It is this option when configuring a pay what you want (minimum = 0) project's price:
Suggested donation — Default donation amount
And for a paid project (minimum > 0), you can configure:
Suggest an alternate default price
Suggested price — Default price shown when someone attempts to buy your project