If they have good evidence of this charge then IMHo, this crap about being wrongly declared insane is an attempt to avoid having people focus on the charges rather than bogus charges of political motivations.
Look at the Jewish Oligarch who fled Russia to England when Putin started rounding up criminal Oligarchs. He spews the same sort of crap about the Interpol warrant he's dodging being politically motivated when Russia has no way to force Interpol to lift a finger. There's solid evidence of his crimes so he works his butt off to keep the focus off the facts.
This could be the same sort of thing since as I understand it anyone in Russia charged with pederasty or pedophilia has to be seen by a psychiatrist before they go to trial. So, at least keep this sort of thing in mind rather than jumping to conclusions. In addition, things like this aren't decided at the national level but by local prosecutors.
It should be an interesting little story to follow, though, given the fact there are local nutcases in office here and there who praise Stalin but I doubt there will be much beyond what they figure makes for good headlines then it'll just vanish like all the successes Trump has vanish.
JMHo
A previous psychiatric evaluation declared him to be of sound mind and a court-sanctioned expert group found no pornographic content in nine photographs of his daughter that are at the center of the case against him, overturning the earlier findings of other experts commissioned by prosecutors. But on Dec. 27, in an unexpected twist, the court ordered that the same nine photos be re-examined by experts for a third time. It also granted the prosecution's request that Dmitriev undergo enforced psychiatric testing to determine whether he has "sexual deviations."
If you have to have politically appointed groups of "experts" examine a few family photos, repeatedly, looking for evidence then, I would suggest, there is nothing there and never was. It does look like they intend to keep on "examining" him until they get the "correct" outcome.