After seeing the replays (and the referee beaming in admiration at Sukhotsky as he raised his hand during the official announcement) it definitely seems to me to have been a "hometown stoppage" - almost on the lines of Calzaghe-Manfredo. That's not to take away from Sukhkotsky - he was definitely stealing back the momentum that the Pole had built up over most of the first five rounds and was rocking him but Kuziemski wasn't anywhere close to being "out" and could have easily rallied back.
Had that fight (Brahmer vs. Sukhotsky) been in Sukhotsky's home country, it would definitely have been stopped by the referee. The referees in Germany try not to stop a fight that would cause the boxer from Germany to lose.