Science is not theology: ideas must be tested against reality.

We thought antimatter would fall down, but it's been very hard to test (since gravity is so weak). In particular, antimatter tends to form as fast-moving charged particles, whose gravitational behaviour is drowned-out by other forces like electromagnetism. Hence we need to form neutral particles, like atoms of anti-hydrogen; and that requires slowing the particles down. Even then, measuring the gravitational effect on such tiny scales requires incredible precision!

That's right, it's usually been theorized that gravity would affect antimatter the same way as regular matter, but it's been hard to confirm as it's a serious challenge to obtain a significant mass of antimatter

The reason you're reading this on some nerd website and not every single news outlet is that this was the strongly expected result - we see photons affected normally by gravity all over the place, we see CPT symmetry hold up everywhere we look, and negative gravity would be hard to square in with a general relativity way of thinking.

That all said, the opposite result would have been huge. We know our understanding of gravity is flawed to a degree we don't know about flaws to the theories of (at a low level) literally everything else we're aware of in the universe.