"While confusing in the context of paying for the car behind you in a drive-through, “pay it forward” means to repay a kindness by being kind to someone else rather than the person who was kind to you."
The article didn't claim it had anything to do with 3x. That was simply explaining the version in the movie, which did in fact popularize the term.
A proper definition of any term should not be consistent with its mis-use. The term from the movie is a ~mis-use, and yet the term as elsewhwere defined (by your quote) is consistent with the mis-use. Its not technically 'false', but it suffers from an 'error of omission', for not having the correct level of granularity (to avoid confusion).
The article didn't claim it had anything to do with 3x. That was simply explaining the version in the movie, which did in fact popularize the term.