Each of the universes that appeared across the DCTV crossover event "Crisis on Infinite Earths" had a specific rationale for their designation, even the Smallville reality, dubbed Earth-167.
While many worlds were named after the year they debuted, like the world of the 1989 Batman film being dubbed Earth-89 or the 1960s Batman television series taking place on Earth-66, Smallville -- which premiered in 2001 -- broke the naming pattern. Taking into account that the main Arrowverse reality was Earth-1, the crossover's showrunner Marc Guggenheim revealed how the production chose to call the Earth-167.
"For the most part, we at least -- as a starting off point -- named the Earth after the year that the property debuted. So like, Flash 90 is a reference to 1990, the year of The Flash television show. With respect to Smallville, it was a decision -- I forget why we didn't use Smallville's premiere year," explained Guggenheim in an interview with Fake Nerd Podcast. "We might have been using it for something else. But Don suggested 167, which I believe is a nod -- I'm probably going to butcher this -- I believe it's a nod to Al Gough's birth year."
Confirming Guggenheim's recollection, Alfred Gough, Smallville co-creator, was indeed born in August 1967, resulting in the alternate designation for the fan-favorite series. Smallville ran on The WB and The CW for ten seasons starting in 2001, before its brief return for the crossover.
"Crisis on Infinite Earths" is available to stream in its entirety on The CW App.