huh...?

[hoennshipperxxx]

He's probably just very handy with ropes. That's the only thing I can come up with. It might be something he got experience in while he still was a wild kid.

he often works with ropes yea... (he makes clothes for his pokemon)

but still my question is unanswered, hoe did he get the rope on the stalectite?
and how did he do all the stuff without her noticing?

 

[Idiot!]

If you read the chapter before the one Ruby escapes, he was lifted into the air by the Swellow, with Zuzu holding on to his leg. As they are flying, maybe Ruby somehow casted the string? And perhaps tied the string when she was too preoccupied with him?