Gamakichi told him to do it, so I'm guessing it was some sort of collaboration technique. Maybe Naruto helped him to jump as high as he did. Idk tho. Good question.
Could have been storing chakra for that huge rasenshuriken too.
Most likely a mistake on Kishi's part sines Jiraiya explain it was a jutsu not requiring no seals at all. He might have refer to having to use a clone for the Rasengan and the shadow clone dose need a hand sign.
I think it basic charkra control with an added elemental affinity, nothing that involves seals. She claps his hand to focus his kuruma and naruto chakra.
If you compare it to any other time naruto used a lot of chakara. i.e chuunin exams. When he puts his hands together it means he is building up chakara. Makes sense because before only one FRS would exhaust him and now he is making a huge one.