Of course, the DSM is very controversial, and many people could fill in the argument, but this article doesn't do it.
Or at least that's the version told in Adam Curtis' documentary The Trap (part 1)[1] which engages in Curtis's usual enthusiasm for fashioning a sweeping historical narrative out of somewhat sparse materials - in this case presenting the "Thud" experiment and its followup as a pivot point in the tale of how R. D. Laing's anti-psychiatry ironically led to the advent of the DSM IV era.
However that may be, if Curtis' account of the followup is correct it seems harder to argue the diagnostic prowess of the psychiatrists was not open to question, regardless of the status of the original experiment.
1: In the section beginning here: https://youtu.be/y97Ywl7RtUw?t=2204