A domestic Concussion Management Review Group (CMRG) investigating the incident decided Northampton wrongly allowed the Welsh winger to resume playing after he sustained the injury in the Premiership game.
The group, however, did not call for the club to be punished.
World Rugby said on Friday it was unhappy with the way the injury was handled since the priority is always player welfare.
"It is ... disappointing that apparent non-compliance with the sport's elite head injury protocols led to George remaining on the field of play when he should have been immediately and permanently removed," it said in a statement.
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"World Rugby's 'recognise and remove' protocols state in no uncertain terms that any player displaying clear or suspected signs of loss of consciousness should be permanently and immediately removed from the field of play."
The CMRG report stated: "The group does not consider that the medical team (or the club) failed to complete the HIA (Head Injury Assessment) protocol nor intentionally ignored the player's best interests".
World Rugby said on Friday though that the HIA should not even have been undertaken given that North had already suffered several head injuries during his career.
"In this incident it is clear there was a failure to comply with these robust and well-established protocols which continue to successfully protect players around the world," read the statement.
The CMRG, set up by England's Rugby Football Union (RFU) and Premiership Rugby, made nine safety recommendations for new procedures to govern future incidents, which were welcomed by the players' union (RPA).
World Rugby also noted its "untoward review incident review process" is designed to identify issues of non-compliance and reduce the risk of future repetition.
It added it would seek more information from the RFU about the factors behind "the apparent non-compliance with World Rugby protocols and the outcomes reached by the independent review group".
The decision by the RFU not to sanction Northampton was widely criticised by former international players on Thursday.
The Rugby Players' Association (RPA) and brain injury charity Headway also took issue with the conclusion that the club did not deserve punishment.
(Writing by Ken Ferris; Editing by Tony Jimenez)
