The news are just in. I am not familiar with the matter, I will post some details now and update this later. At this point, I am trying to figure out what he said, or did. I will form my attitude after the facts are known.
His self-description mentions that he left school, and was into chess, self-education, chasing meteorites and sun activity, and traveling.
Some of his statements which were found on internet:
"For how long Tomsk officials will keep stealing, and the Federal Security Service and Prosecutor's Office - fronting them and prosecute those who disclose corruption?"
"I had the misfortune to be convinced by personal experience that the school is a repressive institution of the state, carving out of the children the gears for their mechanisms, grinding fates, breaking bones. Soviet order required people to be smart up to a point, to believe in socialism properly, and tighten the nuts at factories well. New order was finally formulated; prior to that, teachers were in confusion, whom should they train and prepare, greenhorns for Chechnya, or prostitutes for the oligarchs; but now everything is clear - you need to prepare buyers for supermarkets."
Well, with ideas like that, as those things go in practice, he could end up getting fired from his job (if he had one), for spilling the beans, but it seems to fall a bit short for 5 years in prison ?
Apparently he made other more radical statements, sharply criticizing rebel republics in Donbas (as noted by the court), and apparently proposed 'federalization of Siberia ". Details are not readily available to me at this time.
(To be updated if more information becomes available)
Tiumentsev: "it so happened that they took my books, related to history of Trotsky, Makhno, their own works to be more precise, They also confiscated my notes, (all) up to diaries and poetry. They confiscated my notes on about 10 years of Sun activity, which I kept since 2005, analyzing the data. That was all about science, that was obvious. Why do they need this, I have no idea. They even took my notebooks. Those two criminal code articles, 280 and 282, they were related to videos I have made. My videos..." (recording stops here)
Added ("Day of People's Wrath"). Had a chance to review his other video, Day of People's Wrath, April 2015. This matter turns out to be more complicated than I thought.
In this sharply critical video, Vadim accuses authorities of corruption and collusion with the private sector to raise public transport fares. The video calls for a protest which is planned to be peaceful, but not agreed upon in advance with authorities (as required by law). Mid-way through the video, Vadim gets angry, and says things like 'this regime should go down" and "we, the people, will arrest them and put them up against the wall". The latter phrase almost surely means an expression of strong anger and frustration, not an intent for actual violence, but it is really unfortunate that he uses it, because 'up against the wall' literally means to execute, to shoot.
Thus while I can see where he is coming from, appreciate some of his concerns, have a sympathy to him on a human level, and wish him all the best, it is not like there is no case whatsoever to answer here. The matter belongs to the professionals league, at linguistic, legal, and human rights experts level.
Added. The wonder of social media delivered this joke on my doorstep today: "There are only two sorts of people who are happy with the authorities: the ones not in the know, and the ones having a share" (Hey, I am just translating!)