Any div with a tabindex value of 0 or 1 gets an accessibilityRole of Group. AXWebArea is expected. See test file for example and steps to replicate.
<rdar://problem/22506647>
Created attachment 260318 [details] Demonstrates unexpected role assignment when tabindex of 0 or -1 is added to div
This is actually expected behavior. the idea is that if someone has made an object keyboard focusable, we always want to make sure that it appears in the AX hierarchy so VoiceOver can focus on it. without more info about what kind of object it is, it becomes an AXGroup. you can assign another role="" to that object if you need