Unfortunately Auto-Complete is not supported to validate the inputs from the source list. It allows you to filter the values from the list but also allows you to type anything since it's a free form text input.
You will have to call activity to validate on change of value.
If I understand your requirement properly, it sounds like maybe a pxDropdown is a better control choice for your use case. This way a user is automatically constrained to only choosing values which are from your data source.