Maybe one injection didn't work.
I saw a reversal of a couple of expected side effects a few weeks after one of my Zoladex injections and wondered if it might not be working. I got a testosterone and PSA test done as a consequence, but they came back as expected. I think some symptoms do come and go a bit.
Your friend's case does seem remarkably tied to a specific injection though. It's too late now to find out if it worked or not, unless he had a testosterone test during that period, or maybe some PSA tests before, during and after that period.
I always book the injection appointment with the same nurse. She knows what she's doing. The others probably do too, but I know this one does.