Cardinality Violation during Views contextual filter setup, how to fix this?
Reading the instructions for multiple views contextual filter arguments you get the solution: 


  Allow multiple values:
  If selected, users can enter multiple values in
  the form of 1+2+3 (for OR) or 1,2,3 (for AND).


So if you need an OR operator you should return a string of "1+2+3" and if you need an AND operator you should return a string of "1,2,3".

So don't return an array() but a string.