J-7 mystery !

Me again with a maybe silly question !

Does anyone know why the J-7/MiG-21F-13 was “delivered” to China regardless the Sino-Soviet break in 1960 … at least the negotiations which must have started in the very early 1960s were surely “influenced” by that relationship-cool-down. So was is an attempt to re-warm them as a political attempt/consideration or what’s the reason behind that step (the rising tensions in SE-Asia /Vietnam) ?

Cheers, Deino