I have had this discussion with members of my writing group. Some were more advanced with the mindset of if one writes, then one is a writer.
For me, it was when my first book was published. When I received my first royalty check, it just reinforced what I had told myself.
For many people in our circle, either of those reasons is the bar they set whether that person is family or friend. When one hears that repeatedly it is hard to break that mantra they have for you.
It takes a lot of work to write a book of any size. The easiest part is writing the darn thing. The work you put into a novel is minimal compared to the colossal amount of work left to do on the manuscript.
One still needs to do a vicious cycle of editing, revising, editing again, revising again, publishing and marketing your book.
Considering all that it takes if you write, you are an author. Don’t let anyone convince you otherwise. Only when those people write books of their own will they truly understand and get where the rest of us are coming from to doing this. Maybe if they wrote a book they would not be so dismissive of others.