How Does Riot Choose What Items Get an Icon Change?
Gyazo
I mean seriously look at these outdated Item icons (to name a few) and they change a relatively new item (Introduced Patch 5.22) 
and 
at a glance. Part of it's the rounded nature of the two, having roughly the same radius on that circle, and both being a shade of green (maybe color blindness was a factor as well?) This might be a response to that.