If $A$ is false, then both $A \Rightarrow B$ as well as $A \Rightarrow \lnot B$ are true.
Consider any $X \subset M$.
$ \forall \alpha, \alpha \in \emptyset \Rightarrow \alpha \in X$ is true, since $ \alpha \in \emptyset $ is always false.
Therefore, $\emptyset \subset X$ $......(1) $
$ \exists \alpha, \alpha \in \emptyset \Rightarrow \alpha \notin X$ is also vacuously true for the same reason.
Thus, $\emptyset \not \subset X$ $..........(2) $
$(1)$ and $(2)$ lead to a contradiction.
The second statement is not entirely correct.
The relation $A \nsubseteq B$ means that $$(\exists x) \big( x\in A \, \wedge \, x\notin B \big)$$ but it doesn't mean that $$(\exists x) \big( x\in A \, \Rightarrow \, x\notin B \big)$$