Oh, right — I know what you’re talking about.
I wasn’t in the fandom then, and I haven’t seen a lot of theories about this, so I hope others will weigh in with thoughts and links.
Based on your question, I’m guessing you think and/or are worried that Harry and Louis broke up around this time, and sent out the messages to thank Larry shippers for all their support. And Harry’s door photo (which he posted the same day as his “thank you” Insta — October 16th), presumably, was meant to symbolize the end of the relationship. Since I stated in the introduction that I think we have a ton of reasons to think they’re still together, you can deduce that I disagree with this theory. What I DO agree with is that both of the boys, especially Harry, often use social media to send subtle messages. So I don’t think this was all meaningless.
You’re right, it could be a lot of things. Here’s one alternative theory I’ve heard: Last fall, Blind Gossip suddenly switched from posting tons of blinds about Harry and Louis being together to posting tons of blinds about how Harry and Louis broke up because Harry had cheated on Louis with Nick and become addicted to coke. Blind Gossip is run by someone who goes by the name of Ace. And, intriguingly, the door is located in a place called Ace Hotel.
If it sounds crazy to suggest that the tweet and two Insta photos were actually a reference to Blind Gossip (acknowledging the boys’ awareness of it and hinting that it’s bullshit, presumably), let me run through a brief timeline:
October 15: BG posts its first blind about cheating.
October 16: BG posts a three-part story about One Direction going wild with alcohol and drugs in a Cardiff hotel.
October 16: Harry posts the door and thank you Instas.
October 17: Louis posts his thank you tweet.
Since I don’t think “they broke up” is a plausible explanation, and it’s not unusual for the boys to use social media to send subtle messages, I think this is the best explanation we have.