As per Beer glassware wiki
A tulip glass not only helps trap the aroma, but also aids in maintaining large heads, creating a visual and olfactory sensation. The body is bulbous, but the top flares out to form a lip which helps head retention. It is recommended for serving Scottish ales, American double/imperial IPAs, barleywines, Belgian ales and other aromatic beers. Some pint glasses which taper outwards towards the top are also called tulip glasses, despite having notably less curvature.
So I guess Tulip only refers to the flared top to help capture aroma.