I was reading http://helps.ameba.jp/faq/pigg/5301/post_362.html, and it said "ピグ", I can't for the life figure out for the life of me what it means (Unless it means pig, and contextually that makes no sense to me.)
Normally a typical young Japanese netizen might tell you
ggrks and I did that for you... but it showed no result, as I have expected.
Well, as its a popular Japanese Sim-like game, you can't really say that there's an etymology for this probably. If you still believe so, how would you explain all those spells in Dragon Quest like リレミト? :)
And for your information, there is a Japanese word for 'pig' which is 豚, more commonly written as ブタ, and if you insist to use an English-derived version, then it's ピッグ (the infamous Zombie Pigman was written as ゾンビピッグマン in the Japanese Minecraft Wiki) , not ピグ.