SWH beat me to it.
which 1 engine fails or its rotation is stopped
This is the key clause, in the case of roll-back, did either of those conditions occur? A malfunction yes, a failure or its rotation stopped, hmm? Airbus go to great lengths in their FCOM bulletin to give guidance for the avoidance of unnecessary in-flight shutdowns. More info
directly from Airbus.
Splitting hairs, yes, but there are subtle differences between the regulations & the manufactures guidance creating a large grey area in the case of reduced thrust operation - which is Airbus policy unless a checklist directs the engine to be shutdown.