While the Object Calisthenics principles are:

  1. Use only one level of indentation per method
  2. Don’t use the else keyword
  3. Wrap all primitives and strings
  4. Use only one dot per line
  5. Don’t abbreviate
  6. Keep all entities small
  7. Don’t use any classes with more than two instance variables
  8. Use first-class collections
  9. Don’t use any getters/setters/properties

I am not sure why those rules should be considered calisthenic.

They should be considered a base foundation for coding. If you don’t do those, then you can’t even walk. They are not any kind of calisthenic.

Also, I am happy that the examples are in PHP which speaks that PHP is no more the swamp it was before.