The Soweto giants announced that Sangweni had left the club for the Chilli Boys, with the midfield maestro having endured a frustrating 2017/18 season.
Much was expected from the 29-year-old player when he joined Pirates from Chippa 12 months ago, but he struggled for game time under Serbian coach Milutin 'Micho' Sredojevic.
Sangweni has since returned to the Eastern Cape-based outfit, and Goal spoke to Mokoena about the lanky player's transfer.
"Honestly speaking, I thought Pirates would keep Thami because he is a very good midfielder," Mokoena told Goal.
Sangweni, who spent months on the sidelines due to a knee injury, only made three appearances in the Premier Soccer League (PSL) for the Buccaneers.
"I do not think that he was given a fair chance to prove himself because he only made a handful of appearances for the team last season," he continued.
Mokoena expected Bucs to keep Sangweni as Nyatama's back-up with the team heading into a gruelling 2018/19 season.
"I understand that injuries also hampered his progress, but I expected the club to keep him as Musa Nyatama's back-up in central midfield," the retired midfielder said.
"Musa deserved to play regularly because he was consistent and Thami would have provided stiff competition," Mokoena added.
"Thami is younger and he would have learnt a lot from Musa, who is more experienced. It is rare to find a player, who goes the entire season without sustaining injuries and being suspended," he explained.
"They needed a player like Thami ahead of a long and tough season, but I guess the club has a plan. Surely, there are players, who will provide cover to Musa in midfield," he concluded.