Not all instances are going to be equal in terms of things like stability and uptime. It's going to be unfair and frustrating to users who might randomly end up on a bad instance. It might work if it only chose along the top x instances or something, to ensure a bit of reliability for new users.
It was less about intangible "concerns" and more that most of their time spent moderating was from users of this instance and since they're strained on time, it made sense to simply defederate until the necessary mod tools exist to make things easier.
Historically, it's been known for its security issues and vulnerabilitities.
The "data" in question doesn't really prove anything, there are a lot of different ways to interpret it. For example, it could be that iOS users are generally less technically savvy than Android users so need to look up things more often. It could be that iOS users perform the tasks in question more often than Android users. I don't use iOS so I can't comment on its intuitiveness, but this is really not the best way to show that one is more intuitive than the other.
Maybe they think they're telling on him to the admins
That might be fixed now, I had the same issue on Connect a short while ago, and it's working now. I'm just waiting for Sync to come out for Lemmy.