Yes, that’s my understanding. The markup - i.e. the HTML - associated with hidden elements is loaded, but HTTP requests to load content from the DB are not made until the element is visible. In other words, Bubble is pretty smart about bandwidth and performance in that regard.
That said, it’s still good practice to design pages to be as lightweight as possible as well as to optimize DB structure and queries. As with most programming environments, there’s nearly always more than one means to the same end, and some approaches are better than others.