Should be to the frame.
Honda being a unibody doesn't have a frame. In SCCA and NASA they require a plate welded to the floor pan (or wherever that attachment point is located) with a minimum square inch of footprint, and minimum thickness, and the cage bar is welded to that. I've seen some horrendously hard impacts that totally wrote off the car, and these attachment points have held up.
That being said I hope that car is for drag racing (with a helmet) and is never put on the street. Roll bars in street cars = almost certain death for occupants in a wreck, if your head comes in contact with the bar/cage, which is very likely.