"I am not making this up" is a succinct way to say "this was a really stupid string for the book to contain".
Tptacek could have chosen to say that differently, but it does add value as written. I have no idea what ASN.1 is; simply telling me that the book contains that string doesn't mean anything to me. Telling me that it was a stupid thing to say doesn't teach me about ASN.1 or crypto, but it does teach me about the book.