It means that somebody who is angry about Ubuntu for some reason says that you can't use the word Ubuntu in your programs to test whether they are running on Ub

It means that somebody who is angry about Ubuntu for some reason says that you can't use the word Ubuntu in your programs to test whether they are running on Ubuntu, or Canonical will sue you. There is no real evidence that this is the case. I expect that tomorrow I will hear that Canonical will sue me if I publicly say Ubuntu.