I realise that blue is usually used for inert (or practice) rounds, but there are a small handful of training rounds that have noisemakers associated with them. I believe that you are mistaken when you say there is no fuse in the blue painted practice pineapple grenade you have pictured. Without seeing the shipping container or the numbers printed on the grenade body, I can't with certainty state this is one of the noisemaker practice grenades I am familiar with though.
If it is, the bottom of the grenade is punched out, and a 'short' noise maker fuse (approx 1/2 the charge of a regular grenade), is used to simulate the normal 'time' variant associated with a fused fragmentation 'pineapple' grenade. It is not quite a 'flashbang' however ... it does make quite a loud bang when used for grenade drill ... and ... the user guidelines state it is NOT to be used in an enclosed space, or for drill purposes where it could inadvertently end up going off in a crowd.