"In which case, isn't comparing it to Simulink instead of Sympy a bit ... odd?"
No, as it is not used as Sympy. Modelica is used to model physical systems in a composable way with graphical representation of connections between components. Many people use Simulink for that, so this is why it is compared with it.
Sympy is a nice project, but is applied in a different context, definitely not to model systems with thousands of equations in the industrial setting (that would be painful).
In which case, isn't comparing it to Simulink instead of Sympy a bit ... odd?
It's like coming up with a Functional language, and choosing to compare it to Java instead of Haskell.
In any case, interesting language. It would be interesting to see a proper comparison against sympy / symbolic.
(I spotted this, but it's not really a comparison https://pmc.ncbi.nlm.nih.gov/articles/PMC7924524/ )