Icelandic international Sigurdsson signed for Spurs in 2012 after impressing on loan at the Welsh club.
But he was told his services were not required when Pochettino took charge in North London in the summer of 2014.
That meant he was sold permanently to Swansea, where he has since become a key player in his second spell with the club - scoring 32 goals in 105 appearances to date.
Pochettino regrets Sigurdsson sale
Sigurdsson's sale is a decision the Spurs boss now lives to regret as the Argentine believes he saw what he described as the "perfect player" go on to "develop" after making the switch to the Swans.
Now believing that Sigurdsson would be a great fit in his title-challenging squad, Pochettino felt that "in that moment" things were not working and it was the "club's decision" and "his decision" to make the move happen and allow all parties to "find another way" to develop and move forward.
He revealed that everyone at the club who knows Sigurdsson "talks about him very highly" which isn't a surprise to the Tottenham boss, who claimed that every time they have met he has "shown his qualities" and not just on the pitch as a footballer, but also away from it as a "man."
Ultimately he believes that it is a "shame" the way things have worked out, with hindsight perhaps the decision isn't one he would repeat but Pochettino believes that is "football" and you "never know in football."
Of course, Pochettino will face a visit from the former Tottenham player this weekend as Swansea take on his Spurs side as they continue their desperate hunt for points in their bid for survival.
With Tottenham's current form leaving plenty to be desired, Sigurdsson might just fancy his chances of proving once again why his former club should regret letting him leave.
The Swans are coming into the game off the back of a win, their first under Bob Bradley, a 5-4 triumph against Crystal Palace last weekend.
Sigurdsson has been a crucial part of the limited fortune Swansea have had so far this season, and he'll be hoping to fire once more at his old stomping ground come Saturday.