I would have thought that an urgent inspection would not be required due to the fact that the risk of the reported parameters resulting in an engine failure in the immediate future were deemed to be low.
Also even if the end result was going to be an engine shutdown, losing one of four engines is not an overly dramatic occurrence. It is not ideal or desirable but the impact on the aircraft safety is negligible. As with most 'airline safety' it is about managing risk, the risk here did not warrant a grounding of the aircraft.