I agree it seems like he's letting you know that he wants to go downstairs. I hope you get your repairs done soon. All the best to you.

I go a different direction. I disrupt the act, discover the reason, and provide an appealing and equally disruptive activity with guidance and added stuff. I honestly think it sounds pretty fun, its not harming anything, so I would definitely focus on what it is for, and giving an alternative. misbehaving is really when we're destroying property, so if you put a pillow where things fall, items are no longer crossing that line, and you can deal with it comfortably. :D

Sensory diets if its something he needs to do to self-reg <3

Thanks @Jareka but he cannot access the stairs bc he hurls his body around in frustration and will try to get past the zipper door into the basement which is unsafe with industrial equiment, nails and exposed subflooring. Workers come in and out of the door and need to access the stairs.
I am beginning to think he needs more new creative non object related play activities to decrease interest in throwing things down the stairs. He is very attached to his stuffed animals and it is like having them around is part of the problem.

Good to know - so a clear description of a consequence. This morning, my son somehow discovered how to slide under the plastic zip-door leading to the stairs. My husband was calling his name and couldnt find him anywhere, and lo and behold, discovered him on the steps with his toys. You literally cannot even go to the bathroom without worrying where he is and how quickly he moves. I feel like I have a super smart toddler that is also 7.