In the context of this exercise, is it possible to store multiple values under the same key?
No, this is not possible because keys are unique, and there can only be one key-value pair for each key.
For instance, say that we could actually have multiple values stored under the same key:
hash_map is val1
hash_map is val2
This is not possible, because an index cannot store two values simultaneously. One of the values had to have overwritten the other when adding them to the hash map.