That's not a stupid question, it's an excellent and subtle point. In your example, one of those two is much less baity than the other, so that one is preferred.
What the rule means by "original title" can be any one of the candidate titles that an article itself provides. That can be the main heading on the page, but often that is misleading or baity, especially with media sites. The HTML doc title, as you point out, is often a good alternative [1]. Often a subtitle is better than the main title. Other good candidates can be the URL, a photo caption, or a phrase from the opening paragraph.
When the original title is misleading or linkbait, HN's rule says to change it. In such cases it's far better to replace it with representative language from the article itself [2] than to make up one's own language for it. On HN the principle is to let the content speak for itself, so we try wherever possible to avoid putting words in an article's mouth. When undoing the dirty work of a headline writer [3], put the author back in charge. Don't knock headline person off their perch in order to grab it yourself.
When the obvious options for a good title all fail, you can nearly always find one in the text itself. In fact, it's strikingly rare for media articles not to include, somewhere on the page, an accurate and neutral phrase that says what the article is actually about. I wonder if this is not coincidence, or good writing, so much as SEO. In other words, the very same forces that make headline writers churn out bait to entice users may be driving authors or editors to include accurate summaries to bait search engines. Your mission, should you choose to accept it, is to hunt for the latter to replace the former.
In cases where none of the options for a title produces a good one, including scouring the article body, it's ok to make up a title as a last resort—again, using representative words from the article itself as much as possible.
[1] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
[2] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
[3] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...