“I thought it was 1.31 miles” (half marathon joke)

A half marathon is 13.1 miles. “I thought they said 1.31 miles” (or “I thought it was 1.31 miles”) is a joke that has been printed on many images.
   
“13.1?!??! I thought you said this was 1.31 miles!!!!” was posted on Twitter by LEYDA HERNANDEZ on January 13, 2012. “Best signs at the Detroit Marathon…‘I thought you said 1.31 miles’” was posted on Twitter by Bret Davis on October 21, 2012.
   
     
Wikipedia: Half marathon
A half marathon is a road running event of 21.0975 km (13 mi 192½ yd)—half the distance of a marathon.[1] It is common for a half marathon event to be held concurrently with a marathon or a 5K race, using almost the same course with a late start, an early finish or shortcuts. If finisher medals are awarded, the medal or ribbon may differ from those for the full marathon. The half marathon is also known as a 21K, 21.1K or 13.1 miles, although these values are rounded and not formally correct.
       
Twitter
LEYDA HERNANDEZ
@LEYDAHV
Replying to @erynitaphoenix
@erynitaphoenix 13.1?!??! I thought you said this was 1.31 miles!!!!  😉 Wahhh
11:00 PM - 13 Jan 2012
 
Twitter 
Bret Davis
@fatkid41
Best signs at the Detroit Marathon…“I thought you said 1.31 miles.”
11:33 AM - 21 Oct 2012
   
Twitter
Jëss
@JessDubman
“I thought it said 1.31 miles” 😂
10:08 AM - 25 May 2014
 
Twitter
Ariel Kozicki
@arielkozicki
I thought they said 1.31 miles… #halfmarathon #13.1 #malibuhalf #malibumarathon @ Malibu Half… https://www.instagram.com/p/BbP66PrgpHk/
4:18 PM - 8 Nov 2017 from Malibu, CA
 
7 May 2018, Newsday (Long Island, NY), “LIers win races” by Vera Chinese and Deon J. Hampton, pg. A6, col. 5:
Others motivated themselves through humor. Friends Maria Becker of Bay Shore and Vicky LaSala of Seaford had shirts made up for their first half-marathon, stating on the front: “I thought they said 1.31 miles.”
   
Twitter
Brett Fischer
@brettfischerDPT
Favorite shirts from the @brkgsmarathon (I’m only half crazy not full crazy.):
“If you can read this, I’m not in last!”
“I thought this was 1.31 miles…”
1:35 PM - 12 May 2018