The advice seems to be "keep walking on eggshells" :'(
Well, the question was what is going on. A deeper understanding of the odd behavior is very important to deploy the right tools in the right way. It is also important to know when tools fail. So let's look at this more from a how-to perspective.
It is a common initial misunderstanding to equate avoiding invalidation with walking on eggshells. It is tempting to compare avoiding to trigger (walking on eggshells) with avoiding irritating/emotionally disorienting behavior that is triggering. Avoiding invalidation is avoiding the toxic subset of triggering that does more long term damage beyond the immediate blow-up. Avoiding to protect a boundary (often requiring to invalidate in the situation) and the related major blow up on the other hand would be unhealthy for us and the pwBPD in the medium to long term. When we protect a boundary we accept that a few eggs are crushed.
Consistency in our behavior is key. And as described above without a firm framework it is easy to get lost. The framework is based primarily on Validation and Boundaries which is very different from shooting for the goal of avoiding to crack a few eggs. Both key tools affect in the short term and support the emotional regulation of the pwBPD in the medium to long term.
Back to the situation: Approaching anyone with problems without smalltalk is simply impolite. It is easily startling, surprising etc. which are all activating immediately the fight-flight response system and shutting off reason. In pwBPD the reason is shut off and is usually not recovered quickly. One of the most important intermediate advanced tools to communicate with a pwBPD is SET (Support, Empathy, Truth) which is deliberately structured in a way to put the hard stuff at the end after some relationship building. The fact that the car door was open should definitely be shared but only after "Hello" and entering a SET sequence.
The fact that wife felt ignored is a fact - fair or not. Considering that she was alone some time beforehand and might have something to share makes this understandable. Coming home and wanting to read something is also understandable. Both sides behave natural but the wife is invalidated. As this situation will repeat it is worth thinking on how to avoid this conflict. One way would be for newcmags to deliberately dedicate 15 purely to listening/validation as the first thing when coming home. Another way would be for newcmags to to upstairs and not be visible for a limited time. The latter will be harder on her and I would recommend the former until newcmags has a solid grip on boundaries.
When she finally blew up there was nothing to do anymore - she was beyond reason. Going upstairs was the only healthy course of action left. Distance allowed both sides to cool down quicker than if they would have stayed close. The text messages are an indication that she got temporarily further upset. But they are imho. also a sign that she does not feel listened to. So newcmags dedicating time to active listening / validation might help her in general.