Believe it or not, a A321 from Air China. It is a pretty typical narrow-body cabin, with 4 rows of 2+2.
(In domestic market they don't offer 'Business' and labels this 'First', thus earning 3x points. On international flights this is labeled Business. )
It is popular and usually has pretty high LF. On this flight it was almost full (15/16 seats taken), but that could be because EQ-swap. Flight was meant to be on A332.