The young Demon flew for the grab within scoring range late in the third quarter, when scores were level.
The umpire closest to the contest initially paid a mark, but the umpire in the centre of the ground - around 50 metres away - felt that Howe had not fully controlled the ball.
Gieschen said the wrong decision resulted.
"It was a clear mark," the umpires boss said on What's Your Decision? on afl.com.au Tuesday night.
"We encourage the umpires, if they see something from another zone, to get involved and help out.
"But quite clearly this one wasn't an obvious clear-cut decision for him to make, and if we had have stuck to the umpire who was in that end zone, we would have got the right result.
"So, good on the umpire in the mid zone for trying to help his mate, but we've got to be 100 per cent certain and make sure we get it right if we're going to make a call from that far away."
Gieschen also said Adelaide's Ian Callinan should have been paid a mark in front of goal against the West Coast Eagles on Saturday night.
"Purely a case of our umpire being unsighted here," he said.
"A couple of West Coast players got in his way.
"The ball was controlled by Callinan, it was a clear mark, but unfortunately not seen by the umpire, and he didn't want to guess in that situation."
Watch What's Your Decision? to see both incidents, plus Gieschen's explanation of:
* No holding the ball free kick to Demon Jack Trengove when he tackled Port's David Rodan.
* No free kick for a push in the back to Gold Coast's Jarrod Harbrow after a third quarter contest with Hawthorn's Paul Puopolo.
* Three similar-looking centre bounces at the MCG on Friday night, one of which was recalled and two that weren't.
* An umpire asking Carlton's Lachie Henderson to touch the spare bag of footballs behind the goals before kicking in from a St Kilda behind on Saturday night.
* A free kick to Western Bulldog Lukas Markovic against Fremantle's Kepler Bradley for a push on Saturday.
* A deliberate out of bounds against North Melbourne's Ben Cunnington on Sunday evening.
