One or more of the Drakes had run afoul of Talia al Ghul prior to Tim approaching Bruce and DickTim has an exceptionally messed up relationship with both the al Ghuls but Talia in particular really wants him dead. She spent years conditioning both Jason and Damian to kill Tim, starting long before Tim was ever adopted by Bruce. Damian in particular targets Tim as a threat to his inheritance when Dick is the eldest of Bruce's legal children and therefore should also be one of Damian's targets. It would have been easy for his parents to come across Talia in their many travels, especially since they liked to work on interesting archeological digs, which in the DCU often uncover powerful magical artifacts that would interest the al Ghuls.
WMG / Robin Series