>>2962265Kaji is basically trying to figure out Shinji's reaction, since Shinji's living with the ex that Kaji still has a crush on and the girl he feels protective of. Shinji's reaction tells Kaji that Shinji is gay as fuck and he doesn't need to worry.
(AFAICT, this is also Megumi Ogata's interpretation.)
In their next scene, even though Kaji admitted that he was just messing with Shinji, Shinji is kinda disappointed that their gardening session doesn't count as a date.
