Rumblestrutting Piggy rumble strutting at human

[Redxsilhouette]

Hello! So I'm new to the guinea pig world, just got my piggy in May of this year! But I've researched hours and hours and learned so much before getting my pig. His name is Kurt and he's a rescued "bachelor" pig. The rescue tried for 6 months to bond him with a buddy but Kurt wasn't having it. So he lives like a king in his 8sq ft cage with all the works and floor/laptime regularly and great food.
He's a ton of fun, but sometimes he rumble struts at me and puffs up a bit. It's only happened twice but I can't find any info on what it means towards a human. Both times it happened as he was being petted and it was over very quickly. No biting or chattering.. Just a few rumbles and a puff up. I immediately quit petting and he goes right back to soft weekweeks and nuzzles my hand.. I've read rumble strutting is only for flirting or aggression towards other pigs..
He came from a very neglected life before the rescue got him. Small cage, no other pigs or love from ppl for 2 years is what they said... Is it that maybe Kurt sees me as another pig and is trying to establish dominance?
Again, it's not often it happens. Usually he's all about playing, food, popcorning and kisses. I'm just curious about what he is telling me.

Thanks!