David, I suspect this phenomenon has nothing to do with it being a tissue cultured plant - I expect this is something some individuals can do as part of their natural reproductive process. Just think how easy it would be to miss this phenomenon in wild populations!
Or or maybe some individuals* - once they reach a certain age - can afford the resources to manufacture seeds (an expensive proposition for any plant; they have to have the resources available to make seeds or the plant can die from the effort) and so they can switch gender once they feel able to make seed, which is surely an asset in terms of increasing species survivability. With an average of 7 males to every 3 females in most species found in situ, adding a few more females to the equation - especially healthy, robust adults that can afford to make copious seed - would be a real asset, wouldn't you think? So . . do you happen to know if your friends hamata was an older, fully established adult plant or not?