Two declared candidates, Karl Schilling (who announced within the hour of Kevin McCarthy's resignation) and Joe Henry, dropped out and endorsed Meyer. A third possible contender, Felix Gallagher, had not formally announced.
UPDATE: This Civic Skinny item explains everything:
Word is that Marshalltown’s Mark Smith, who bested Des Moines’ Rick Olson, 24-20, in the caucus vote to succeed Kevin McCarthy as head of the Democrats in the Iowa House, has let go McCarthy’s key aide, Des Moines City Councilman Brian Meyer. The move has surprised — and upset — some Democrats. …In a footnote to the race in this solid Democratic district, the Republicans announced their nominating convention for September 4, same date as the Democrats. The Republicans also had a convention in this seat last year. In one of the wackiest moments in a very wacky year for Iowa Republicans, they literally nominated an audience member - and he was actually a better choice than the announced contenders. Story never gets old.
The election proper is set for October 22. Still wondering why, in a seat that's entirely in the Des Moines city limits, Terry Branstad didn't just combine it with the November 5 city election. That worked in 2001 in a Cedar Rapids seat.