The SCAG was published November 2015, Hero was published in 2016 October. Yarin wasn't a thing before that. Which is to say its clear that they put Yarin into the SCAG to set the stage for Hero, its undoubtedly supporting the novel before it came out a year later, without spoiling the ending.
So its clear that this isn't some attempt to retcon Hero, because Hero is why Yarin was King in first place, just like the remains of Tymanther in the SCAG too Erin M Evans future novels into consideration, setting them up, without spoiling key events.
Which tells me that its simple as someone but very little effort into that part abd just copy pasted the SCAG instead of doing their research. This entry doesn't ignore Hero, it can't because the SCAG's entry was based on Hero itself (the start of the novel, not the end). How utterly careless again. I'm dropping my rating if the books to a 6. This isn't a retcon, its just sloppy work. There great parts of this books like Calimshan & the Atlas of Faerun (although even that has some errors), and then there is just where it really feels like they put far too little effort in like Damara.