The guard may dismount but do they become "combat shy" as per rule or is there an omission as in the list you can take dismounted "regulars" who are not combat shy ?

it seems strange

yes they do become Combat Shy as they follow the dismounting rules of page 185 like any other troops with Dismountable where the list does not specify anything different. Comparison with the dismounted option for the other Timurid cavalry is not valid as they are replaced for the whole game/comp by infantry which is not the same thing as having the Dismountable characteristic.