Not necessarily. Double entry bookkeeping catches errors in cases where an amount posted to one account does not have an equally offsetting post in another account or accounts (i.e., it catches errors when the books do not balance). It would not on its own catch errors where the original posted amount is incorrect due to a mistaken assumption, or if the offset balances but is allocated incorrectly.
You probably know this but, for anyone else who is interested, the easiest way to get a feel for Icon nowadays may be through its descendant Unicon which is available at unicon.org.
Yes, the article appears to be a short excerpt from a book and probably loses a lot of context because of that. I am interested in the questions raised by the author but will wait for the book to come out. The good news is that it appears the book will be open access - MIT Press seems to be encouraging this lately (at least by allowing this as an option for authors).
Forth started as Chuck Moore’s solution to the problem of how to bring up an interactive programming environment on hardware with limited memory. The base of the system used a small number of primitives written in assembler or machine code upon which more complex functions were built. The genius of the system was that you could easily bring it up on different hardware by translating the primitives, which was quite helpful at a time when software was frequently customized to the hardware (which itself was not as standardized as today). Nowadays Forth is probably most useful on embedded systems.