Dykask,
You seem knowledgable so I'm asking...
If PRT's PoW algorithm is quark, why is PRT GPU mineable?
Because someone wrote smelterMiner... But it is questionable thing and for quarks only. At least, it was... What exactly used for PRT GPU mining? I found nothing...
I'm glad you answer that questions! I haven't dug into the mining code for the quark ... but in general the idea behind scrypt was to prevent GPUs from being used. Programmers are often very clever.