According to my accountant, the IRS defines a startup as a business activity that is not yet profitable, but you're actively working to make it profitable.
By either of these definitions, not every new venture is a startup. This is just semantic. I don't think "not a startup" should be an insult.
EDIT: I see from another comment that Merriam-Webster defines start-up as a fledgling business. IMHO this makes the English language a little less rich, since you could just as easily say "new business", but it is what it is.
A startup is a 'Useful infrastructure' previously and wholly 'nonexistent' that 'fills a need' for a population and thus earns revenue. I'm sure I've left something out but this definition helps me sort between startup ideas and content ideas in my head.