Both Vne-2kts and Vs+2kts are within the aircrafts envelope but we dont deliberately fly there on a commercial flight.
If said captain was training he may not wish to inflict a potential tailstrike hazard on his/her trainee for example.
There may be many reasons for this. Not least inaccuracy of the load sheet. If the sheet is only accurate to the extent of the information on it (most use standard weights for pax and bags etc..) you can not be 100% sure that you are in the envelope, especially when you are that close to the edge.
If he had any doubts I think he did the right thing.