Tell me exactly what I did wrong.

[Dom R]

Her experience with her BF has revealed that he expresses his love/affection via acts of service.
....
there's nothing wrong with choosing not to spit on or discount what he does offer, nor is it an indication that she doesn't get the concept.

What she said in her post, went further than that, though.
There was a whole context/concept in her posts that, to Lillie, someone's love language defines both how they want to hear "i love you" and how they speak it.
That they are one and the same.

Here's where she explicitly goes even further opposite from what the book says:

YOUR Love Language is the way you habitually express love and generally people make the assumption that others' LL's are the same as theirs.

The first part of what she wrote, is completely backwards from the "cause and effect" from the book (The "and generally..." bit meshes with the book, though)

The book defines your love language, as the way that you want to RECEIVE love. Not "the way you habitually _express_ love".

Yes, I completely agree, that the book mentions that people by default, most often "habitually express love" in their love language. However, someone's "love language" according to Chapman, is defined as how they want to receive it, not the way that they express it.

The way that they express love, tends to line up with their love language. but it does not define their love language.