I am not too sure about the specifics of tantric sex, but as you said, it is to control ejaculation by delaying climax or making it subside.
What happened in TS story was that semen was blocked from coming out when the point-of-no-return of climax was reached (based on the points quoted),
which can cause back-flow of semen leading to infection (
last point under causes of retrograde ejaculation).
He also felt pain. I hope that should not be the case if real tantric sex methods was used.
Just wanted to point out the cause and dangers (e.g. infections & infertility) of
retrograde ejaculation, especially if a lot of people read this story.
Thanks for a great sharing of experience from TS. Hope to hear more soon.