addAttribbuteToFilter size doesn't match with the object in side it

Question

I tried to use the addAttributeToFilter like the example below:

$_productCollection = $block->getLoadedProductCollection()->addAttributeToFilter('discontinued', 1);
echo($_productCollection->getSize());
echo($_productCollection->count());
foreach ($_productCollection as $product) {
    echo($product->getName());
}

The attribute discontinued is a yes/no field. The origin $_productCollection has two products and one of the product's attribute discontinued is set to be yes.

The first two echo are 1, but the echo in the loop prints productName1 and productName2. I think the filter should be working but somehow when I traverse the for loop, all products are printed out. How is this supposed to happen?