What it isn't, as far as I can see, is 'taking credit for someone's work who you didn't respect'. Firstly, 'xandering' refers specifically to Justin's theory and method for developing non-linear dungeons. One of his reasons for wanting to change the name was that people kept thinking that his system was created by Jenelle. Secondly, the blog series on xandering, and I assume the book, repeatedly credit Jennell for developing some of the first non-linear dungeons and popularising that style of dungeon. He isn't trying to take credit for anything she did, only for his own content.
Happy to hear arguments to the contrary, but right now I don't see Justin taking credit for anything other than his own work, and he's been very clear about Jennell's influence on it.