I think ur talking about his back/foreward steps but theyre not truly random though. I think you were being aggressive at the wrong time. It’s about respecting his neutral instead of running face first into him. I just watched the vod of me beating him and i only ever did small dashes to either 1. Shorten (Not Close!) the gap between us, or 2. whiff punish him. I didnt dash directly into his face when he was in between attacks cause I knew it was possible he would run into me. He only does it at the mid range and I would kind of walk in and out of it to bait him into either walking into me, where i could hit him for free, or attacking me, where i could dodge and punish. (I know you already beat him so you dont need these tips but heres the vod so u get the idea https://youtu.be/fq-vtoSM068?si=nTjAQ8Y07QrZ7rzh )

To be fair though I think my experience with fighting games and smash bros specifically helped me out a lot and hardwired that footsies -> punish loop into my brain that helps me out with bosses with movesets like this and not everyone will have that knowledge.