particle は - は significance in ゲームは上手いですね

I'm confused by the reaction to は in this exchange

A:「ゲームは上手いですね!」
B:「ゲーム「は」.....」

source context: http://neetsha.jp/inside/up/1/2/12840/24.jpg

Answer

A:「ゲームは上手{うま}いですね!」

B:「ゲーム「は」.....」

This is the contrastive 「は」 or at least that is what B takes it to be.

A's line can be interpreted as "You are good at games (if not anything else)!", which is exactly how B interpreted it. That is why B reacts (jokingly) by emphasizing the contrastive 「は」.

B's line is obviously difficult to translate literally as English has no such particles. In that sense, A's line is already difficult to translate to begin with.

Particles can be so powerful that this shortest exchange can stand as a valid joke in itself. (And this often takes place with the contrastive 「は」 in real life.) The 「は」 in B's line would receive much stress in actual pronunciation.

B could have also said:

「ゲーム『は』って・・・」

「ゲーム『は』かよ！」

「ゲームだけかよ！」