Is that not the point of having the splitting feature? Conversations have a tendency to drift, and it’s seldom obvious in advance that an offhand comment related to the topic will turn into its own discussion. For this thread, the topic was how assignment behaves. I made an offhand, but on-topic, observation, that = means equality and not assignment in maths, which lead to this thread.
It’s great that you split it off, that keeps the original threads topical but leaves a link so someone who wants to read the full evolution can do so. The alternative is doing that manually, which would take a crystal ball: In some parallel world there was one or two comments about :=, which wouldn’t be out of place in the original topic thread, and that was all.
Us mere users can’t gather up posts and bundle them into a new topic, so starting a different thread once it’s clear that we’ve drifted into some new interest means posting a new thread, posting a link to it in the old thread, and posting a link to the old thread so people can catch up on the conversation. This is an inferior version of what the moderators do anyway in breaking a thread off.
I recognize that it’s extra work in what can be a thankless task already. Does moderation have permissions fine-grained enough that you could deputize a few regulars to have the thread-split functionality without the more powerful (and abusable) moderator privileges which go with it? Because I don’t think lecturing people about staying on topic will be effective, topics change, which is why the thread-splitting power is so useful to begin with.