(Komi is a rule in go that exists in the modern era, but did not exist in the Edo period. This kid appears to be using a style of play from the Edo period.)
My attempt to translate:
That move, since it was a time when rules were different from the modern era and there was no Komi, was considered to be the best move.
At first I thought ちがう was attached to コミ ("different komi") which did not make sense to me; so I think it was actually attached to 時代 making it a noun with two phrases attached to it, but I could be wrong about that, so
あの手は "That move" (topic)
現代とはルールのちがう[時代] "[time] when rules were different from the modern era" (first noun phrase. actually this phrase confuses me, what is とは doing here)
コミのない時代 "Time when there was no Komi" (second noun phrase) (I think の replaces が here?)
だから "because it was" (creates dependent clause)
好手されたのだ "[it's the case that] it was considered the best move" (main comment)
So I guess I have two questions:
What is going on in 〜とは〜のちがう phrase and why is it arranged that way?
Is it correct to parse this as two noun phrases attached to one noun or am I on the wrong track?
Fake Edit: ran のちがう through eow.alc.co.jp and realized it's just parsable as 'different' but I am still confused about とは and not sure if I'm right that のちがう is attached to 時代