Hi,
I believe the sights shown in your picture are more typical of a Firestorm 380. The Firestorm 380 and the Bersa Thunder 380 are virtually identical. They're made in the same factory, by the same people, and are imported by the same company but they have different rollmarks. About the only significant difference is the rounded trigger guard of the Firestorm and the squared off, serrated one on the BT380.
Maybe a sight got pulled from the wrong parts bin?
I'm a Bersa newbie so my idea might not hold up but hopefully you'll find it helpful.
Dan