The DPRK is in an unusual and tenuous position, and there is very little that can be usefully gained from speculation that doesn't involve considering that. At the same time as trying to develop a [dictatorship of the proletariat/highly unusual set of political economic arrangements], they bear constant acts of sabotage from the South and the US that are at times extraordinarily depraved, have endured sanctions for decades, and suffered from regional poverty since long before the WPK took over, all the more so after the US bombed them back into the stone age.

Given this context, and probably also the Otto Warmbier incident, we can begin to understand why they would be vigilant -- some would say hypervigilant -- towards various security issues, and don't want some jackass tourist going rogue and causing an international incident. Since they never made a ton of money from tourism -- especially discounting Chinese tourism -- sacrificing some level of profitability to their tourism industry to keep tourists on a short leash and prevent incidents isn't so inexplicable.

Complete aside, what nationality is your tourist friend? I assume not American because -- due to US passport law -- it is very difficult for a US citizen to gain access to the DPRK since the Warmbier incident.

Of course the DPRK is strange, even its most ardent supporters would tell you so, but the fact of the matter is that what westerners think about the DPRK isn't "The DPRK is weird", it's "This is a completely backwards place with absurd laws and propaganda which considers human life worthless," right? "State propaganda says the Kims don't shit and Kim Il-Sung invented the hamburger. Kim Jong-Un had his uncle eaten alive by dogs for being rude to him. The rats eat the kids and the kids eat the rats." etc. My biggest point of emphasis is that every one of those stories, which have agglomerated together to create the hazy cultural consensus that I mentioned, is unambiguously false and you have very little left that you've ever actually seen about the DPRK if you subtract all of that.

Here are some things to look at if you like. Obviously I would not tell you to take anything uncritically and I have my own issues with things here and there. I'd be happy to discuss any of them.

https://www.theguardian.com/world/2015/oct/13/why-do-north-korean-defector-testimonies-so-often-fall-apart

https://www.youtube.com/watch?v=3V4Hnl7J9H4

https://www.youtube.com/watch?v=2BO83Ig-E8E

https://www.youtube.com/watch?v=IBqeC8ihsO8

And of course, you can actually look at statements that they put out:

http://kcna.kp/en/article/q/5a9ffe6e4d6704ac1838b14785365295.kcmsf

Or the fact that the Korea-watching industry is just completely shameless about putting out the most harebrained nonsense with very little pushback (including things that don't make it to the headlines), which really does not lend credibility to the idea of serious-minded criticism of the DPRK having any strong presence in anglophone media and therefore anglophone culture. On this point, because it is a "death by a thousand cuts" situation, it's really just a question of how many examples you want.