I'm sorry but if I induce a 10deg NU input on an aircraft flying M.8 the climb rate will come on pretty much as the input is applied. We simply don't know enough to ascertain (data wise) to make anything sensible out of that statement by the BEA. For all I know it can just be lost in translation.
The only reason why I can see an experienced Captain/Crew maintaining a NU input with stall warning going off is that they believed that the aircraft could not be stalling (it's an Airbus right?) and therefore deduced that the warning must be erroneous.
Mode and Law confusion are the most common things that pop up in the simulator:
'Wtf is it doing now'' seems to be a common phrase.