This is not meant to slight Pittsburgh or Buffalo, but to illustrate the terrible nature of Nielsen ratings. There are about 111 million television households. Roughly 1.1 million in Pittsburgh market.
There are reportedly 40,000 Nielsen boxes in the entire US. If Nielsen distributes them at the percentage of television households, it means that there are 400 or so TVs in the Pittsburgh market with a Nielsen box. Assuming every TV was on, it means 10 of the 400 Nielsen TVs were tuned to the Pens game. This means that especially in small markets one or two of the Nielsen TVs account for a huge portion of that number.