It's simple, it's the difference between something being canon, and something being confirmed as canon. Tifa and Cloud are canon in the sense that, when the developers are writing the story, that is the story they are writing. When deciding on Clouds actions and motivations they're following the "Cloud love Tifa" versions of the characters. If you look at the big picture that is always the direction the story flows towards.
But when you write a story there is always wriggle room for interpretation in everything, some developers go out of their way to say "no, that's wrong, THIS is correct", but the japanese aren't really like that. If you have a different interpretation than the developers, that's fine. They wouldn't go out of their way to tell you Aerith and Cloud aren't a thing, but they wouldn't go out of their way to tell you Cloud and Sephiroth aren't a thing either. But Cloud x Sephiroth is still a fanon, it's not canon, or a reasonable interpretation.
The HA dates are the most obvious example of this. Tifa and Cloud are romantic, that's the story being told, so SE makes them kiss. In the story being told Aerith and Cloud are NOT romantic, so they don't kiss. But SE still knows that a lot of people wish for Cloud and Aerith to be romantic, so they give enough wiggle room that it doesn't interfere with the canonical story, but still allows people to daydream. He holds her hand, in the story as written that's him indulging her asking him to indulge her, but it's also some breadcrumbs to tease "heej, who knows, maybe it's more!" for the people who like to imagine such things.