No, it doesn't seem to be a common phrase. In most fandoms, we usually hear about things like 'canon vs fanfic' or how fanfic is inspired by the original work. This phrase 'azir stepped on fanfic' is so specific that it would probably only be known within a very small group of fans who are familiar with both the Azir character and the particular situation where this phrase might apply. For example, if Azir is a relatively new or niche character, it's even less likely to be a common phrase across a large fandom.
Most likely not. Fandoms tend to use more general terms to describe the relationship between the official content and fan - made works. Phrases like 'the official story influenced fanfic' or 'fanfic expanded on the original' are more common. 'Azir stepped on fanfic' is an odd and very specific phrase that doesn't seem to follow the typical patterns of fandom language. It might be something unique to a particular storyline or event within a very specific part of a fandom.