I'm finding it hard to believe. A random soldier from, as he said, super highly guarded and well-performing nuclear millitary base just happened to get away with a proof, to go and tell western media how highly trained, guarded and prepared the nuclear facilities are? If it's genuine, I highly respect that, but I still suspect that especially given what we know about the state of russian army, and how they operate mostly through info wars, I'd wage it's more of a "he was send here to talk about how amazingly preared the nuclear bases are".
If the overall tone of the message is fearmongering (see, russian nuclear bases are super guarded and can launch nukes within a minute, that they maintain daily!), then it's probably just a setup by ISB.