Here's your clew (sic) that the article may not be so reliable: It credits the FBI's linguistic analysis for locating the Unabomber, when in reality, it was his own brother who said “hey, it sounds like Ted.”
Articles at the time noted that a significant part of the ongoing investigation was the FBI linguistic analysis of the manifesto but that the brothers own reading led to the identification. This article seems to be shading the story.
I don't totally agree with you but I see where you are coming from. The article states "Eventually, the linguistic evidence was strong enough to issue a search warrant..." which could be referring to the brother pointing out the similar writing style or the FBI's assessment pointing to someone from Chicago. It's not clear.