They took two different universe models, neither of which match the one we live in, and mathematically produced the same black holes. The key differentiators being that one universe has gravity and multiple dimensions while the other has no gravity and 1 single dimension.

While the article likes to take a logical leap and assume this supports the theory that our universe is a hologram, what was actually proved by this numerical experiment is eloquently explained in the article's quoting of theoretical physicist Leonard Susskind.

"They have numerically confirmed, perhaps for the first time, something we were fairly sure had to be true, but was still a conjecture — namely that the thermodynamics of certain black holes can be reproduced from a lower-dimensional universe"

- Leonard Susskind