This looks to be a questionable measure of Internet Access service provider's throughput.
I'm quite puzzled as to why USInternet (a mostly private fiber based access provider) had the same exact outage times as CenturyLink (probably doing ADSL services). When I know USInternet doesn't depend on CenturyLink's infrastructure. I don't think they reach to Duluth or Eden Prairie or Cloquet either. So, we'll just say that they may have some overlap in their data.
Otherwise, I'm going to guess that this data is obtained via some agent on consumer computer's connected to the Internet pinging the services central point.
There's way more ISPs in Minnesota than three cable-cos and one telco, and one private fiber provider.
But anyway, I'd guess this is purely "pings" over the Internet, and not surprisingly enough all vendors have about the same level of "outages" reported. I wouldn't put much faith in this. Or the Internet in general to always deliver every packet put into it.