Godaddy is unpredictable. Nobody knows how do they check availability. The same happened to me with domains dropped 1-2 days ago, empty whois output, available everywhere - but not available at godaddy.
Also, be careful with ownership transfers at godaddy. When I sold daddy-registered domain last time, new ownership details never appeared at whois as the domain disappeared from their whois. Godaddy support are dummies, it took them 3 days to correct this. However, one week later the sold domain was mystically returned back to my account and ownership changed back to me. I had a good luck with the buyer though, they had experience with me before (so trusted me), but they are now urgently transferring the domain away from godaddy.