Yes, in that he finds her diary entries in which All Is Revealed (By Means Of Cute Interludes About Kittens, Soccer, And Female Bonding Via Cookery). If you mean, did he know before jumping in that box with her (I must be the only person who uses the boxtank because she specifically says she loves it)...a) it's an optional 'mission' so whether you play it before or after reading her diary entries (or not at all) is up to you, though it does first become available before you can start finding her diaries, and b) in any case it's the other way around - she jumps him.