In the last few episodes, Nkunzi had a flashback of the night he was poisoned and almost died.

The memory was so vivid it caused him to freeze and space out for a few seconds, and once he gathered himself, he started murmuring Putin’s name.

If you can remember well, Nkunzi had a visit from Mondli, who asked him to say the name of the person whom he suspects of trying to kill him.

After flashes back, he starts realizing that Putin is not the one who tried to kill him; if he keeps flashing back to that night, then he will remember that Sbu returned to the house after he and Mr Thwala passed out.

Sbu came in to boast about killing Nkunzi, and Mr Mthethwa was a casualty in the matter; he was dead, but Nkunzi was just unconscious.
Watch Nkunzi having flashbacks below: