Calc's "AutoInput" feature is using other values in the same column to provide possible completions, so, if you're seeing incorrect values, you may want to correct them where they appear elsewhere in the column. As Villeroy points out, the feature is useful to help you enter repeated items consistently.
As for the help, open Calc first, then you should find it from the menu, under Help > OOo Help, or press F1.
Select the "Index" tab, then enter "auto" in the "Search term" box. You should see the topic list scroll to match your typing. Double click the topic "AutoInput function on/off". On that page, you'll also see a hyperlink to a related topic, "Tools - Cell Contents - AutoInput", which has all the details on using the feature.
AOO4/LO5 • Linux • Fedora 23