There is not difference. The default smileys of the forum are quite ugly and there was one called "Cheesy". When I created the new ones I added "Smile" without realizing that the "Cheesy" one was already there using the same file name as the "Smile" one I added.
When I realized that after a while it was too late and both had been used. I always planned on running some SQL command to replace all the 'cheesy' ones by the 'smile' and delete 'cheesy' but just never sat down and took the time to do it.