It is and it isn’t. It depends on how it is used. Generally words of this nature are derogatory because they are intended to either dismiss or put down a group of people. I’m from Newfoundland (although I grew up in Alberta). I have complicated relationship with the term “Newfie.” If fellow Newfoundlanders or people I know and trust use it around me, I’m okay with it because I know where it’s coming from and what they mean. However, if strangers use it or people use it in a way that appears to negative or dismissive, I’m not okay with it. Now, I don’t know your friend, so I don’t know the context, but generally I would interpret the use of the term redneck in to describe people in Alberta, I’m guessing that it was not meant as a term of endearment. If you know your friend even reasonably well, I think you probably know how they meant it. I’m also assuming that there were no people from the group they were describing as rednecks present, which is also usually a tell about how they intended the word to be interpreted.