I've never heard anyone define memory safety that way. You can segfault by overflowing stack space and hitting the guard page or dereferencing a null pointer. Those are possible in languages that don't even expose their underlying pointers like Java. You can make Python segfault if you set the recursion limit too high. Meanwhile a memory access bug or exploit that does not result in a segfault would still be a memory safety issue.

Memory safe languages make it harder to segfault but that's a consequence, not the primary goal. Segfaults are just another memory protection. If memory bugs only ever resulted in segfaults the instant constraints are violated, the hardware protections would be "good enough" and we wouldn't care the same way about language design.