Francesca Eastwood -- Burnt Birkin Wasn't MINE!!!

Clint Eastwood's daughter's been taking serious heat -- as in death threats -- for burning a $100,000 Birkin handbag just for the art of it ... but now Francesca Eastwood wants everyone to know it wasn't hers.

When we asked Francesca about the controversial pics last night, her photographer BF Tyler Shields quickly took the bullet ... saying, "It was my bag, I paid for the bag." Shields wouldn't say exactly how much he dropped, but confirmed the Birkin cost "more than a car."