Actually, 100% branch coverage says every line has been executed but also that every branch has been both taken and not taken. So e.g. every non-constant if statement is both taken and not taken.
Or even if you have a ternary operator (which has an implicit if-then-else take/don't take branch) that is usually only one line.
void foo(int arg) {
int *x = malloc(sizeof(int));
if (arg) {
free(x);
}
}
Not all combinations are tested, all branches are both taken and not taken, but not all combinations of taken/not taken are tested.