If I'm reading this correctly, it will take the curr_line of the previous decompile call.
https://github.com/mahaloz/decomp2dbg/blame/6d47e087b2e9e15be722ee9e04e9840b10e45ab1/decompilers/d2d_binja/server.py#L91-L93
However, the previous call may have been to a completely different function.