Da**, so that kid either;
A: Is a careful schemer who used the MC to get a safe haven while he secretly cultivated (Nothing inherently wrong with that, was a good transaction for both of them, and if he's that clever he might make a good subordinate later)
B: Had some fortuitous opportunity (Which the mc could i'm sure benefit from himself on his next return)
or C: Was kidnapped, possibly by the same person who took the treasure girl sister?
Or some fourth thing im not thinking of.