they said Rasengan was based off of a Tailed Beast BombThese attacks had nothing to do with the creation of the Rasengan or Rasenshuriken but I don't doubt for a moment that Kishimoto made them look similar on purpose. There are a lot of visual references like that in Naruto...
Minato probably saw a Bijuu do it on one of his adventures and based Rasengan off of it