In manufacturing of beverages (and many other products) there is a little thing called acceptable fill tolerances. That is the deviation about the displayed volume on a package that is acceptable. When a machine mass fills packages (in this case cans) it is never 100% precise all the time and therefore there needs to be acceptable tolerances set in place. In this case, you have a can that is 4% under it’s displayed volume, it is likely to be equally possible that you find a can with 169 ml’s of beer, that is 4% above the displayed volume. Since the manufacturer of a product can’t open and examine every single package they produce, they extract x amount of products from a production run and test these samples for their fill volumes to ensure they have enough evidence to make the assumption that all (or most) packages produced are within the acceptable tolerance. Although 4% sounds like it might be outside of the tolerance range (I don’t know, I don’t work in beverage manufacturing), it is possible that all samples picked from the lot to be tested were within the acceptable range and therefor the lot was released.
Long story short, you got shorted 1 tablespoon of beer in a consumer product that is mass filled by a machine. Stop your b**ching