Right. That is what was found. It was enough for them to determine if it was marijuana - or not. Unless it was laced. But, 16 grams of pot was enough to see, yet they called it an ‘unknown narcotic’.
Maybe it was a powder. While a tablespoon is roughly 1/2 of a fluid ounce, most powdery or flaky things have a much lower density than water. So it was probably several tablespoons that they found.
My bet is that it was some synthetic. You don’t “take” pot orally over dinner. It would be like chewing dried garden leaves. Ugh.