Well it looks like the blowout was close to ND/OSU. ESPN/ABC Nielsen numbers include streaming. NBC uses another firm to measure their streaming. Apples to apples ND/OSU is a little bit in front but it's still impressive that a blowout Colorado/Oregon game can basically match 2 high status programs like OSU/ND in a close down to the wire matchup.
From the article:
Saturday’s Colorado-Oregon college football game averaged a 5.2 rating and 10.03 million viewers on ABC, marking the largest Nielsen-measured audience of the season. The Buffaloes’ 36-point loss averaged a higher rating and larger Nielsen-measured audience than Ohio State-Notre Dame on NBC later in the day, which averaged a 5.1 and 9.98 million.
Keep in mind that NBC uses a separate measurement service — Adobe Analytics — to calculate its streaming audience. (For the other networks, including ESPN and ABC, streaming viewership is included in Nielsen’s figures.) Including the Adobe-measured streaming audience of 605,000, the Ohio State-Notre Dame game had a larger audience of 10.58 million.