Speaking as a Filipino, I have never heard of the name 'Plastina' at any point during my history education, even in university classes. The Philippines has also not had any 'kings' of any sort since the colonial period, so that part is a wash, unless he's referring to the Moro peoples in Mindanao. '50 years ago' puts us right in the presidency of Ferdinand Marcos and the Martial Law era, so your friend may be referring to that period, but given the sheer lack of any pertinent results that Google gives me, I wouldn't be sanguine about it.

I'm thinking two things: either your friend is making stuff up or he's misremembered the name. The possibility remains that he might be telling the truth, but there's some serious holes in that story that I'd put this as one chance in ten next to the other two.