The simple answer is: Who knows? The interpretation of this particular paragraph has been really $/*)%#*^%. Confusion appears to stem from a statement put out at the national level early on and later retracted!
The information at the link you gave appears to be incorrect under the
current interpretation.
1. The rules do not mention a "backstop".
2. The dimensions apply to the "egg mount" (Para. 3.c.)
3. The egg will be secured to the egg mount with tape (Para. 3.d., Sentence 2)
4. Tape pay not be placed on the front or rear 2cm of the egg (Para. 3.d., sentence 3)
5. Both ends of the egg must be exposed to view (Para. 3.d., sentence 4)
In my mind there no possible way to make the arrangement in the referenced drawing comply with these requirements.
This is a case where you really MUST contact the organizers of your tournament to see what page they are on!
Here is the complete text associated with the referenced drawing on the North Caroline Website:
Rule 3. c. should read as follows: The egg transport must have a rigidly attached egg mount with a vertical backstop that is rigid and unpadded with a flat surface at least 5.0 cm x 5.0 cm and at least 1.5 cm thick. The horizontal portion of the egg mount which the egg rests upon must be rigid and unpadded, but no minimum dimensions are given so long as it meets requirements of rule 3.d.
**exception to rule 3.c. If a team wishes to be nationally competitive, they will not be penalized in NC for removing the backstop. In this case, the dimensions given will apply to the horizontal portion of the egg mount.