Theplanet merged with EV1 and then with Softlayer (which is the name they continued operations under) until they were eventually acquired by IBM who still owns and operates Softlayer.
I believe that any account with them that had a dedicated server on the monthly bill previous to 2010 used/still uses IP addresses from address blocks that The Planet Internet Services paid the original fees on.
As to why that has never been updated with ARIN, I do not know though it is odd as IBM has owned Softlayer since the middle of 2013. Maybe ARIN doesn't have the mechanism to change the registration name without automatically whacking them with the 64,000 dollar bill for initial netblock registration of the size I would guess they had, kind of like cutting corners to scale up the same concept of a grandfathered phone plan being honored so long as you don't change the plan. Who knows.
xF goes through CloudFlare which most definitely suffered an outage recently in various parts of the world. We noticed specifically that CloudFlare was not accessible in the SE USA, Miami area particularly.
If the server/host/datacenter, etc. where xF is hosted goes down, you "should" still get something from CloudFlare, either stating that the site can't be reached, or it's trying to server a cached copy, or what have you. If it was just plain down and wouldn't come up, the issue is either on your end or a CloudFlare outage of some sort.