It could be but it is also possible that you had a random non-functioning injection - was it injected in the same place as usual, by the same person? Did it feel as it normally does? There have been recorded incidents of injections failing due to incorrect storage, incorrect placement, missing the muscle, being given a 1 month dose rather than 3 month, etc. Have you taken any other medication / supplements recently (prescribed or otherwise) that could have interfered with the hormone injection?
If any of the above, the PSA should drop again with the next injection so I can see why the onco wants to wait until after that.