The phrase "Lines should not exceed 80 characters or glyphs" occurs in the section "Intent of this Success Criterion". The actual text of the Success Criterion says:
1.4.8 Visual Presentation: For the visual presentation of blocks of text, a mechanism is available to achieve the following: (Level AAA)
Foreground and background colors can be selected by the user.
Width is no more than 80 characters or glyphs (40 if CJK).
Text is not justified (aligned to both the left and the right margins).
Line spacing (leading) is at least space-and-a-half within paragraphs, and paragraph spacing is at least 1.5 times larger than the line spacing.
Text can be resized without assistive technology up to 200 percent in a way that does not require the user to scroll horizontally to read a line of text on a full-screen window.
Source: Understanding WCAG 2.0, SC 1.4.8
At first glance, this could be seen as more prescriptive than the original quotation: "is no more than" instead of "should not exceed".
However, the preamble includes the phrase "a mechanism is available to achieve" where "mechanism" is a "key term" defined at the bottom of that page as:
process or technique for achieving a result
Note 1: The mechanism may be explicitly provided in the content, or may be relied upon to be provided by either the platform or by user agents, including assistive technologies.
Note 2: The mechanism needs to meet all success criteria for the conformance level claimed.
One "mechanism" (provided by my Windows 10 platform) is to resize the browser window. If that is done, the site seems reasonably responsive and re-flows the text to match the window, allowing you to choose your own maximum width: