Kapu is just someone SL identified as having the potential to play international cricket but as, SL's domestic comp is of a significantly lower standard than most other nations, (club cricket is the main domestic cricket there, with very brief comps where teams are organised into much stronger districts) most young players tend to get blooded in the international arena before they are anywhere near ready to play at that level.
his averages are climbing year by year. It's just that, as a 23 year old international (or 20 when he first emerged) people may have the impression that this is because he is some sort of prodigious talent, it's not, just they reckon he'll be up to standard with a few years experience and full time coaching (far fewer full time pro-contracts in SL as well)