I did a search to find out if Next ever actually made a bike called "Top Banana," or if that was a custom decal.
Turns out the builder was inspired by an Instructables post, and left a comment with some of those same pictures 12 years ago (scroll down to the bottom of the page):
Top Banana Bike
Good eye, Unca Sam. That is indeed a caster bearing.
Now you can build your own "Top Banana"...