  CSS100217 was a nuclear, rapid and luminous flare in a Narrow-Line Seyfert 1
galaxy, whose initial interpretation as a supernova is now debated between
variability of the active galactic nucleus (AGN) or a tidal disruption event
(TDE). In this paper, we present and discuss new evidence in favour of a TDE or
extreme flaring episode scenario. After the decay of the flare, the galaxy
entered a long-term low luminosity state, 0.4 magnitudes lower than the
pre-outburst emission in the V band. We attribute this to the creation of a
cavity in the accretion disk after the tidal disruption of a star in a
retrograde orbit with respect to the accretion disk rotation, making a TDE our
favoured interpretation of the flare. We also show how the host galaxy shows a
point-like, compact profile, no evidence for an extended component and a
relatively low mass, unlike what expected from an AGN host galaxy at z=0.147. A
compact host galaxy may result in an increased TDE rate, strengthening our
interpretation of the event.
