The rule will be activated when the number of line items(products and not quantities) is equal to or more than the specified number.
Each individual products is considered as a line item in cart.
The rule will be activated when the number of quantities in the cart is equal to or more than the given number.
It is possible to provide a tiered quantity based rule by creating multiple rules with a range like at least 2 quantities and less than 5.
So, discount applies when the cart has 2-4 quantities. Creating another rule for 5 or more quantities.