Am I being unreasonable

Without knowing the full story, its kind of hard to really comment. If she's on the spectrum, then of course there needs to be certain methods used to help her. However, I will say that I think its important you and your partner find some kind of compromise here. If he is implementing a punishment and you then come behind him and undo it, it kind of is undermining him. And its not going to teach the child good behavior. Now whether binning the toys was a fair punishment or not really depends on more context. Im sure the solution is somewhere in the middle. Maybe he's being too strict and you're being too lax. But take my comment with a grain of salt because there is so much we on the outside don't know.

Any idea when she will be evaluated for autism? Does your partner doubt the possible diagnosis all together?

In my opinion, i really think it depends on the particular child and their capabilities. Ive known plenty 6 year olds who are able to tidy their room (put toys on a shelf or in a tub) etc on their own without help. And sometimes they will notice that one parent is willing to bend and do more for them than is necessary. So they take advantage of that and the child gets away with doing less on their own. But of course, im not saying thats whats happening here. Depending on if/where she lands on the spectrum, she may not be able to do so on her own. So does he just think she is capable of doing it on her own and you don't? Does he think you're spoiling her or does he acknowledge the possible diagnosis?

How is he with the other child?