1. They have a policy of marking apps as NSFW if using them has a high probability of loading NSFW content onto the device. We can't easily rule this out. It's a small project so they have to be reserved about compliance issues because they don't have the resources to defend against expensive litigation and they could just be exercising an abundance of caution.
2. They're trolling Republicans with malicious compliance. They don't like the laws being enacted, they know the people enacting them like the Bible, so they apply the policy in the way which is maximally adversarial to the opponents imposing it on them. "If you don't like the consequences of your law then feel free to repeal it."
Which one of these is even objectionable? It seems like you want that if they're doing the second one they should admit to it, but in that case they're just maintaining kayfabe. The trolling is more effective when it's ambiguous. It's obvious that it could be that. If the message is to invite their opponents to go eat sand then it's not being lost in translation. But making that explicit only makes it easier to dismiss them as antagonists, or retaliate against them for being overtly defiant.
Whereas if they play it straight, what is someone going to say? That it shouldn't apply to this, right? Okay, then we need to pin down the rules for how exceptions work. Exceptions that could then be applied to other things. Which is to their advantage to have their opponents doing in this context because then they want the exceptions to be broad and reasonable instead of not caring if someone else is getting screwed by them.
Not only is this not going to convince anyone that there's anything behind it other than an attempt to formulate a winning argument (having set that as your goal) irrespective whether there's any actual sincerity to the words you're choosing, but it's going to come comes across to a healthy portion the world's population as the opposite of clever: that anyone who's convinced themselves that it really is clever and that no one can possibly permeate this forcefield of insincerity is a perhaps-delusional, and definitely-insufferable halfwit.
The original complaint was that if they were doing it to be controversial, why not do the same thing to viewer apps for Reddit or Wikipedia? But those are necessarily distinguishable. If the standard was that a viewer merely could load external NSFW content rather than was likely to, you would have to do web browsers, mail clients, podcast managers, file transfer apps, video players that can open external links -- it'd be most of the repository. And that would be far less defensible, because you can point to specific controversial Bible verses, but how are you going to make the case that generic FTP clients and web browsers are NSFW with a straight face? But conversely, how would you argue that a Reddit viewer is NSFW but a web browser that can open Reddit isn't?
The fork where they need "a sincere belief that these apps contained content unsafe for minors" was the other fork, where they're doing it because of potential liability rather than to make a statement. But that fork was flawed to begin with, because they're not required to think that it actually is unsafe. They could also be concerned that someone else could claim that and then even if the people claiming that are jerks and even if the jerks could ultimately lose, they could prefer to be risk-averse when they don't have the resources to handle things like that.