In Naruto anime episode 468, Asura is shown to be using a Rasengan based jutsu against Indra. If I'm not wrong, the Fourth Hokage Minato invented Rasengan several years later. Am I missing something here?
It may not have been rasengan, but just gathering chakra and rotating it for more power. My defense of this would be Indra's using a similar jutsu to chidori in this filler arc. Both jutsus are similar to the modern day jutsus we know, but not quite the same
One hypothesis that can be presented is that a large no. of jutsus had been created in the past but their knowledge and techniques might have got lost with time.
I think it was just to show how Indra and Ashura are similar to Sasuke and Naruto. Like how Indra's sharingan is the same as Sasuke's. And that Ashura inherited the Truth Seeker Orbs like how we see Naruto with them.