If you feel like laying everything out for the full forum will help go right ahead...
Yours is one of many cases where we could provide an explanation of moderation, given permission to do so. Thanks for allowing it. Remember that you can use the Contact form to ask why your post was moderated, and get a full explanation in private. That message goes to the administrators, which gets you not only an answer but a review of the moderation. Exchanging PMs with one moderator would bypass that review, so using the Contact form is for your benefit.
In your case, the thread in question was about Twitter blocking third-party apps. Your post mentioned Saudi money for financing, state entities having a vested interest in controlling communication, the Arab Spring, and a claim that many leftists congregated on Twitter.
You said above that what you posted was "absolutely not political," but the moderators thought otherwise. This post was deemed to be about politics and/or social issues, the type of post likely to take a news thread off topic. Allowing it could have broadened the scope of the discussion, but that broadening is a double-edged sword that can turn a news thread into a political discussion that others users may not want to wade through. That's the reason for the rule, and why we have a separate forum for Political News, where the editors specifically allow those discussions when it's so inherent to the topic.
You mention that your post was based in "provable facts." That's fine, and if it wasn't delving into politics it would have been fine whether or not it had provable facts. The moderators do not confirm or dispute claims of fact, and rely only on the forum rules. It would be untenable, and unhelpful to the forum community, if the moderators were to be tasked with deciding what claims in a post are true or false.
Finally, you said that you received a "stern warning" that "came out of left field." I think you'll find that the moderation message that you received was polite, saying "This is a reminder from the MacRumors moderator team to avoid making posts that are about political, religious, or social issues, outside the "Political News" forum, and that are likely to steer discussions to those types of topics." The message went on to explain the reason for the rule, tell you where to get more information, invite you to use the Contact form if you had questions about the notice, and it ended with "Your cooperation is appreciated."
You may have felt that it came "out of left field" because (a) you didn't consider your post to be political and (b) you're an excellent forum member so getting a reminder was novel.