what you describe is not a found set. I don't have time to click links and download your file, but I think that if you enter search text and only one record is listed in the portal, you want it to be automatically selected for you. This could result in selecting unwanted data after mistyping search text, but to answer the question, Thus, you might want to pop up a dialog asking for confirmation here or some such double check.
if this is a filtered portal, this would be tricky to do as it would not be simple to determine that only one record passes the filter. If method uses an older method where a fairly complex calculation field is used as a match field and the portal is not filtered, a calculation using count could determine that there is only one record showing in the portal and then a script performed via script trigger on the search field could auto select the single value.