As I mentioned in comment to that question, for me the fundamental issue is that it asks about outside the universe. That leaves us with no useful way to answer, as outside the universe is simply a concept physics (and astronomy) cannot usefully address. Indeed anything we don't know of now that could be outside of what we call the universe would, once generally accepted, become part of our model of the universe. There's no "outside" to discuss here and any response is de facto opinion based.
Is it acceptable for me, having provided an answer, to edit the question so as to remove the "opinion" and focus on the presumed intent of the OP?
I have learned not to try and work out the "presumed intent" of people asking questions. Experience has taught me that people, particularly those without a basic grounding in the "vocabulary" of science, often ask questions that don't properly reflect what they want to know.
But it's up to the individual to decide in each case if they feel they have an insight to the question that others do not.
Don't edit a presumption in.
This is obviously my opinion, but I think that many people, especially new users, would be intimidated or very annoyed to find someone else editing a question in a way they don't agree with. This is particularly important for experienced users editing other people's questions as users with high reputation have their edits appear without having to wait for approval. That's very disconcerting to a new user when it happens.
I would always suggest making recommendations or suggested edits in comments, unless that's impractical. Wait for the OP to either indicate agreement or do the edit themselves.
Is it because, having asked whether a particular solution might explain the expansion of the Universe, the OP offers the opinion that this solution "makes sense to me"? If so, this is an absurdly literal and hard-nosed reaction.
I tend to follow the practice on Physics SE and would view this as a "personal theory" which would be off-topic there. There's no such rule here, of course, so I tend to more liberal about it on Astronomy SE, but I with the OP asking about "outside the universe" and an existing explanation (FLRW expansion) already existing, this is another reason (from my point of view) to vote to close.
The question is currently running at +3 votes and has two answers (I declare my interest: one answer is mine) each of which addresses the underlying question, i.e. could the expansion of the universe be caused by something "beyond"? It's perfectly reasonable to question the assumption of a homogenous isotropic Universe, or whether string theory, branes and extra dimensions might be involved. How is that "opinion-based"? And how are the two answers "almost entirely based on opinions, rather than facts, references, or specific expertise"? That, frankly, is insulting.
It's how democracy works on SE.
I've answered questions myself that were subsequently closed for a variety of reasons. This is simply the way a democracy works - you get to take part in the process, but just because it doesn't work out the way you think it should doesn't mean the system is flawed. The people who voted to close don't think it's flawed. It's a win-some-lose-some thing.
I can't do anything to stop you feeling insulted by a close vote that you feel reflects on your answers. An answer may, however, be a reasonable attempt to answer and still not be sufficient grounds to change someone else's (equally honestly held) view of the question as being opinion based.
Fundamentally String Theories and others cannot be proved or dis-proven and lack any evidence to back them up. They are, by any reasonably definition, opinion based. That they are require a great deal of knowledge to discuss authoritatively does not mean they are not, with reference to the original question, opinion based.