Why did this pilot have his single-engine license revoked?
Lets break this down as best we can. 

For starters you've made an error in your assertion. The pilot hasn't had their license revoked, just simply their SEP rating. There's a difference. The person in question can still do their day job as a pilot, on a type-rated aircraft. They have accepted a suspension of their Single Engine rating.

On some finer points mentioned in the linked news article:


  [...] both pilots and passengers do not use shoulder harnesses 


The Indonesian Aviation Regulations specify


  For small civil airplanes manufactured after [27 December 1993], an
  approved shoulder harness for each front seat.


If we make an assumption that this flight was carried out in an aircraft manufactured after 27th December 1993, then both front seats should have been equipped with shoulder harnesses which should have been worn. Hardly the crime of the century, but there you go.


  Second, Vincent gives flying control to unauthorized people


This one is a bit tenuous, unless the PiC has an instructor rating he is "officially" not supposed to allow someone else to manipulate the controls. Finding exact wording to back this up is not easy. I think most pilots (of light aircraft) have let their passengers have a go at the controls. 


  Third, he was deliberately maneuvering zero gravity


This in and of itself isn't the problem, I suspect the problem was whether he was doing so in an entirely safe manner. He gave no warning to his passengers that I could see, and I'm not convinced he performed the checks suggested before such a manoeuvre that would make it safe.

They could easily just cite the following:


  No person shall operate an aircraft for the purpose of air navigation or for operations on
  any part of an airport (including areas used by those aircraft for receiving or discharging
  persons or cargo), in a reckless or reckless manner so as to endanger or be likely to
  endanger the life or property of any person.


The wording of this regulation is fairly similar across many aviation regulators, and is often cited for "You did something against regulations".

Sources:


CIVIL AVIATION SAFETY REGULATION - Republic of Indonesia