Mmm, scientific click bait titling. More accurate would be "Physicists demonstrate a theoretical subatomic structure in simulation". That's important, to be sure, but it has nothing to do with demonstrating the existence of a particle - we've determined something "should" exist based on simulation and data-interpretation plenty of times, and many of those have ended up being wrong. And that's good: good science comes from discovering what _isn't_ true, but that makes it all the more silly to have this title on the article. We've got the simulation worked out... now we need to see if it holds up to reality. It might not. If so, that's valuable information.
Apparently you didn't read the article in full before criticizing it. The article says that the simulation was used to verify real world observations from a particle accelerator experiment in Japan.
"Verify" is a strong word. The RIKEN experiment didn't come close to the usual standard of evidence for declaring a new particle exists, it just showed a reaction for which creation of a tetraneutron is a possible explanation. There need to be a lot more experiments (different ones, not just repeats of RIKEN's) before anybody would be willing to declare tetraneutrons "exist".
Simulations don't "verify" physical findings, they let us tweak the parameters under which we might encounter findings, and now we're not done:
1. practical observation (optional)
2. a hypothesis (either from first principles or to explain a practical observation)
3. testing that hypothesis
4. establish as theory if it holds up, or mark as "known to not be true" if it doesn't.
You've not scienced until you're done with step 3, because step 2 on its own cannot "confirm" or "verify" anything found in step 1.
The most important part is to confirm that a theory is not accidental, giving simulations a disadvantage: it is far easier to accidentally find parameters in a simulation than it is when you're on paper from first principles - even if that paper's Mathematica or R. You can always find some set of values, parameters, and functions that result in the thing you're looking for, so once you find such a set, you then still need to go back to the lab, verify that it holds up, and have others verify it holds up, too.
(the result of a single study is merely a very interesting anecdote. It's not data until your findings can be reproduced, and it's not a scientific theory until it's proven to hold up. Until then it's just a hypothesis)
