"It's a clear mistake.. it's an error of judgment. They (England) should have been awarded five runs, not six," Taufel, a five-time ICC Umpire of the Year, told foxsports.com.au.
The ICC refused to make a comment with a spokesperson simply saying, "The umpires take decisions in the field of play with their interpretations of the rules and we don't comment on any decisions as a matter of policy."
Taufel, a highly-regarded ex-Australian umpire, is now a part of the MCC's laws sub-committee that makes the rules governing cricket.
Law 19.8, pertaining to 'Overthrow or wilful act of fielder', states: "If the boundary results from an overthrow or from the wilful act of a fielder, the runs scored shall be any runs for penalties awarded to either side, and the allowance for the boundary, and the runs completed by the batsmen, together with the run in progress if they had already crossed at the instant of the throw or act."
The bizarre incident took place in the fourth ball of the final over at the Lord's.
TV replays showed Adil Rashid and Stokes had not yet crossed for their second run when Guptill released the ball from the deep.
However, on-field umpires Kumar Dharmasena and Marais Erasmus added six runs to England total following the incident -- four runs for the ball reaching the boundary plus two for running between the wickets by the batsmen.
Taufel also defended the officials.
"In the heat of what was going on, they thought there was a good chance the batsmen had crossed at the instant of the throw," Taufel said.
"Obviously TV replays showed otherwise. The difficulty you (umpires) have here is you've got to watch batsmen completing runs, then change focus and watch for the ball being picked up, and watch for the release (of the throw)," Taufel said.
"You also have to watch where the batsmen are at that exact moment."
He acknowledged the call "influenced the game" but added, "It's unfair on England, New Zealand and the umpires involved to say it decided the outcome".
(With PTI Inputs)