Normally after alternative landing gear extension you have two chances to verify correct down and locked, via the normal Landing Gear selector lever lights and if alt gear extension was performed, also via the downlock verification switch which indicates the related gear is down and locked . This is a infrared system that is independent of the regular ldg gear advisory system...so no, one cannot assume gear is locked down in absence of at least 1 green from either system.......maybe the snippet has it wrong.....