What makes fleur de sel different from regular salt?
I'm not 100% sure but I found this site that explains what fleur de sel is. It says that 


  Like other sea salts, fleur de sel is harvested by evaporating sea water. However, to harvest fleur de sel, workers gently skim the top layer of the sea salt from partially evaporated pools, before it sinks to the bottom again. These salt crystals are very fine, light, and delicate, and must be handled with care and exposed to minimal moisture, or they will clump again.


It looks like you are reproducing how fleur de sel is made, through boiling the water which is the equivalent to "evaporating sea water".