There is no evidence that Sony didn't know about this before the announcement, and statements made by Bethesda indicate that they did, therefore it can be reasonably concluded that Sony is at fault.
If you're going to give Bethesda the benefit of the doubt, then at least have the decency to extend the same courtesy to Sony.
The only thing we know so far is that Bethesda's released a statement and Sony hasn't. Both companies will have their own best interests in mind, but the significant difference is that Sony has absolutely no reason to give a fuck. It's not like they promised mods on their console and even if they had, it's hardly a loss on their part; Fallout 4's sales are gone and done and even if Skyrim: Resurrection doesn't sell they'll probably hardly register it.
Bethesda, on the other hand, did promise those features, and one of their recent releases even makes it an entire selling point; even if Sony was to blame, there's no way they wouldn't lie about it.
Not telling the whole truth is pretty much their thing, if you haven't noticed.
Bethesda's reputation's been taking some serious hits as of late; if they don't recuperate soon, they might lose a significant portion of their income.
Either way, if we only take into account what Bethesda stated, it still seems pretty vague. They've asserted that Sony didn't want to give the players total freedom, which I presume translates into concerns over IPs and mature content; however, Bethesda did the exact same thing if I recall correctly, so I doubt it's that. It's also worded a bit too favourably for them in my humble opinion, so I'm rather suspicious of it all.
As for the "strong source" shown earlier in the thread, I can sort of understand how that deal wouldn't work out. Quality control for every single mod would be an absolute pain, especially if it's unpaid; I'm pretty sure Bethesda wouldn't want to risk paid mods again right now when the entire reason people wanted them was that they were
gratis.
I also understand that Sony would want some sort of standard, presumably predicting that if any problems arose, they would be the ones to get flooded with complaints. It's a bit of a deadlock situation, but it can't be all that there was to it.
It's interesting to note that Sony seems to understand the complications of modding consoles better than Bethesda does, but I digress. That's just my bitterness acting up again.