NoLens: Why are you pressing Enter? I've never done this or seen this done in training. When you say "Pic 2 is me having typed that file in the search field, before hitting enter," I see the file appear in your list, so the filtering is working. That text field is actually for filtering bin content, not searching.
However, it is odd that your exact filter entry (DFLM0637) reveals assets with names other than "DFLM0637" in them. When I filter on an exact asset name, only that asset appears; as I delete letters from the filter entry, more assets appear in the list because they match the new filter. I just tried this myself (in latest release of Premiere Pro 2018, ver. 12.0.0).
Before filtering:
After filtering: