In their defense, if you watch the video, that is exactly what happens. They just begin assuming that every NPC is going to screw them over.
The result is an outcome that is worse for everybody: the DM’s twist doesn’t land because the players expect it, the repeated betrayals are unrealistic, gameplay becomes somewhat predictable, and the players are metagaming by assuming every major NPC introduced is secretly evil.
This is why I think one of the most important pieces of GM advice I ever heard is one we published in the first edition of Adventure:
You get what you reward.
If you want players to have their characters act boldly, you have to have bold actions succeed at least as often as hesitant and defensive ones rather than smacking them down via unchallengeable NPCs and situations. If you want them to choose diplomacy and reward curiosity in interactions, you have to have reaction tables or their equivalent that skew away from hostility or a full neutrality toward reciprocal curiosity and willingness. If you want players not to spend a really long time in planning huddles, you have to reward plans and decisions made quickly, maybe even some fortune/story/drama/etc points.
Many GMs don’t do as much of this as they think - and this includes me. Looking at a record of your decisions throughout a session can turn up habits you didn’t notice and that players may or not be aware of consciously but that lead them to act in ways you wish they could shed. And, to nobody’s surprise so deep in this thread

, it’s another thing that benefits from explicit talk with players. What decisions do they make because they feel they have to rather than because they want to? What can you do to make stuff they want to and that you want them to feel accessible and worthwhile? And so on.
And a side note: I have dozens to hundreds of food and environmental allergies as a side effect of various internal disorders. So I have a lot of experience declining things. This is how it usually goes:
A: Here’s a snack.
Me: Oh, sorry. I can’t eat that.

A: Really? Why not?
Me: Allergies. Goes with the autoimmune thing we were talking about earlier when trading bad doctor stories.
A: Oh, right. Dude, that sucks. Is there something you can do?
Me: Sure. I’ve got this in my bag and brought enough to share / yeah, that other thing would do great / honestly, I’m good, just give me something to drink / etc.
A: okay, can do. And let’s swap some mail before next time and plan out something that works for everyone.
Me: I’ll be on it.
That’s what mutual good will can do. And from what I’ve seen, it can go similarly for Jewish and Muslim friends, vegan friends, and so on, as long as nobody comes with butt pre-stick-ified. So many of these things never become a big deal unless someone other than the person with the nerd insists on escalating them.