Shooter should have declared the malfunction and safely grounded the revolver.
TO should have waited until the end of the stage to verify the position of the unfired round in the cylinder (SDQ if under the hammer).
If the TO had simply advised the shooter to safely stage the revolver instead of reholstering it, THAT would have been considered "proper coaching" to avoid the possibilty of a SDQ = No RESHOOT.
Shooter should have appealed the miscall up the chain of command & received a RESHOOT for RO interference:
SHB p.20