They Dont "Expand" from their shrunken size, they get restored
instantly, there is no pushback because there is no speed here, its just an instant restoration to their normal size
if we take the non instant interpretation, then you would have to cope that not only is this statement false, But that Jigen can expand the rods while their inside naruto and sasuke and cause damage, which would mean he could have
Reverse-Vored them, expanding until they literally explode (he can enlarge them to kurama sizes so theres no size copium)