Usually you can interpret it the way you want. However, I think it is very clear that you either need 3 years or Five years to apply for Citizenship. I don't know where you get 5 years to apply for Indefinite? (I thought we were discussing Citizenship) If you want to make it harder to understand that is up to you but it is very clear in black and white from Home office.
I think you were also logically thinking of 4 and 6 years. Good luck and have it your way. As long as you get what you wants, who cares if it is 3 or 5 years(As Home Office says) and 4 or 6 years as you understand.