Relationship between Deterministic Finite Automata languages
There are a wealth of set theory symbols that are in wide usage. I have seen or used most of those symbols .

In particular, "$L(M) \supset L(M')$" means $L(M) $ is a superset of $L(M')$, but $L(M)$ is not equal to $L(M')$. This is consistent with the explanation given by Wikipedia. To be more specific, it means all words in $L(M')$ are in $L(M)$, but at least one word is in $L(M)$ but not in $L(M')$.

A simple example of that situation can be the following. $M'$ is the finite automaton depicted at Wikipedia example with $S_0$ being the only accepting state. $M'$ accepts words with even number of 0's. Let $M$ be the same as $M'$ except that both states are accepting states. Then $M$ accepts all words.