It simply means it was approved for sale at some time in the past. That could mean it still is, or it could have been removed or purchased before they even had an approved list. So it really means nothing.
To sell a handgun to someone in CA from out of state the gun needs to be legal to be purchased in CA from an FFL which you would have to transfer it to first since there is federal law on out of state purchasing of handguns.
It is not legal to import a gun for sale into CA if it is not on the approved handgun list. It would also require a 10 round or less magazine.
It does not matter if it was purchased in CA if the owner is no longer a CA resident. Private party transfers (which still go through an FFL in CA) only apply to residents of the same state. So if he moved back to CA and was a CA resident again then he could transfer them to whoever, both on list and off list guns that comply with mag capacity and don't have "assault weapon" features.
However as an out of state resident now the guns he has are no different than any other gun out of state. They must be on the list to sell them to someone in CA. If they are on the list they can be tansfered through an FFL, as required under federal law for interstate handgun sales. Otherwise you cannot sell them in CA.
The only time a gun would be worth more is if you move from another state into CA, become a CA resident with nice guns that are off the approved list but otherwise legal in CA. You would have to pay $19 a piece to legaly own them in CA as a new resident, and could then at a later date transfer them to anyone within the state.
If you are not a CA resident however that does not apply. So as a resident of another state his guns are not worth anymore in CA than anywhere else. Considering he bought them in CA to begin with they are probably also not something that would command a higher price in CA than elsewhere.
So no, they are actualy worth less in CA than out of state guns purchased someplace else that are off list in CA (if he moved back to CA and later sold them in CA.)
They are either legal to sell to a CA resident if on-list, in which they are no different than that same gun for sale already in CA and not worth more, or they are off-list and illegal to transfer to CA to be sold, in which case they are worth $0 on the legal market in CA.