It just means that it has more bacteria in it than usual. Milk always has bacteria in it. Pasteurized doesn't mean sterilized. That's why it still has to be refrigerated. Sterilized milk is that ultra-high temp or UV treated milk that comes in a box on the shelf (not usually in the US).
But they're not harmful bacteria. I wouldn't worry about it.
As for the post about expiration dates, it's so true! If you read it carefully, it actually says, "Sell By." So if a store has to sell a gallon of milk by Sept 3, does that mean that the person who buys it on Sept 3 has to drink it all before midnight, or it will instantly turn rancid? I think not! The Food Pantry actually has a license to use and distribute food after their expiration dates. It doesn't go bad instantly on that date. There's a huge buffer built into the expiration dates.