It's because of your query - the LIKE '%searchString%' part.
The %'s at the beginning and end means the query will display all results containing the word entered.
for example, if you enter mint then because of % at beginning and end, it will return all words containing mint such as spearmint, myminto, etc..
Get the idea?
so if you want it to return mints then remove the last %.
Read up on the php manual on the % (wildcard character).
Kevin.