If the testimony is not made up, and I have no reason to believe so, then Ivanov was advised to stop speculating. Why?
I am thinking that his speculation could filter all the way back to the home of the hikers by way of returning college students. Further, if we use the party game of telephone as an example, each retelling of the story gets filtered by each reporter's perception. It is conceivable that an unsubstantiated rumor of lights in the sky could morph into a botched Soviet military test.
It could also be that Ivanov was reminded of his role in the investigation and how his handling of it might play out in terms of career advancement. So, casual speculations with companions could have more gravitas because Ivanov was the one to say it. It matters little if it is factual or not, it is about who said what.
Then, there is the matter that Ivanov found out something of the truth. That truth would somehow involve the deep pockets of the Soviet government,meaning someone is going to lawyer up and go to court and sue the Bear. That, in turn will rile the populace and the lid could blow off the whole thing. To give any credence to this idea, one would speculate that the debris were picked up and carted away before the first rescue and perhaps without the knowledge of the hikers being in the area. After all, the event need not happen in their midst, only in the vicinity.