Of course, this could just be the WB trying to save face a bit. With the movie only being in theaters a week, they're not about to admit defeat so early...
The PR is over as of the last big full page newspaper ad this weekend. What they would do now is get quiet and noncommittal, and place the project in turnaround a few weeks or months down the road - businesspeople don't have to "save face" before the public in this context (they're not politicians and the interests they serve aren't much swayed by chatter) and certainly nothing is served by talking anonymously - "sources close to" etc - about a sequel. If anything that makes them look foolish to their peers unless they actually have plans (which may also make them look foolish, but in that case at least they have a reason to risk it).
One operative question is just how committed Warners is to the notion that they have to mine their comics properties to create franchises in the next ten years - they don't have very many ways to go, there. If GL doesn't work you can bet no one's going to greenlight The Flash.