I understand now about random and sequencial. I like the song example. But I do not understand why array and vector still is sequencial?
an array is a random access container. One way to randomly access it is:
for(int i = 0; i < size; i++)
array[i] = i;
which is sequentially.
another way to access it is this:
for(int i = 0; i < size; i++)
array[rand()%size] = i;
it may not make much sense to do that in a program, but it is perfectly legal.
therefore, by example, a random access container MAY BE accessed sequentially, but it does not REQUIRE the user to do so.
All that to say yes, array and vector are BOTH random and sequential access.
If the site says that lists are the same as array, the site is no good, find a better site.
maybe
https://en.wikipedia.org/wiki/Sequential_access
https://en.wikipedia.org/wiki/Random_access
if you want to look at it from a more pure side,
then think of it this way: a container requires sequential access, or it does not. If you want to make THAT distinction, then arrays and vectors are not purely sequential access, but a linked list would be. Not sure what that means for a tree or graph, though. I am not sure this is a useful direction to go in, though, unless you are doing a thesis about it. I think saying an array is both is fine and would stick to a more practical way to define the terms instead.