The small stage is probably because they're performing for the Super Star K3 Japan Audition
They did their 1st round auditions in Osaka (6/12) and Tokyo (6/19).
Today is the start of the second round (6/25-26).
If I'm reading this right, they send the top 10 acts to Korea next month to compete in the Korean audition.
The winner of the whole shebang gets their Korean debut, 300,000,000KRW prize + 200,000,000KRW record contract, and will have a special performance on the Mnet Asian Music Awards.
Something like 1.3 million people auditioned so far.
Here's some images from their auditions: