Is PCR a DNA cloning technique?
Short answer
All of your sources are correct as they are not mutually exclusive. PCR is used to isolate and amplify DNA to yield small quantities of pure target product. Gene cloning can subsequently be applied to scale the production of the fragment up. PCR thus can be part of the DNA cloning process. 

Background
Cloning in general simply means duplicating. Cloning in Biology refers to 


  [Making] an exact copy of an animal or plant created in a laboratory from the
  animal’s or plant’s DNA


source: McMillan Dictionary

Gene cloning, as far as I understand refers specifically to the isolation of one single gene and inserting it into cells to amplify it: 


  The production of a lineage of cells all of which contain one kind of DNA fragment of interest derived from a population of many kinds of DNA fragments.


source: Northwestern University 

PCR is a technique to amplify a specific strand of DNA that can be used to subsequently clone DNA into host cells (source: New England Biolabs). The cloning is done to upscale the quantity of DNA. PCR uses primers and can be used to isolate and amplify the DNA up to the scale it is easily clonable.