I dont know much about that stat (and its standard values, especially on 50NL FL) but remember that it is connected with villain's calling range (eg. Cold Call 2Bet PF etc). If the calling range is very narrow (pocket pairs), cbet raise would probably indicate a set. On the other hand if calling range is wider (suited connectors, pocket pairs) it may be a semibluff. Actually on mikro stakes I see lots of people raising cbets with a flush draw to slow down the cbettor and to be able to see turn card for free. Thats all I can think of.