My guy, try Google. The world is at your fingertips

"Also unlike first round picks, teams do not receive a salary cap exception specifically for their second round picks. These players must be signed using cap room or an available exception (see question number 25), such as the Minimum Player Salary exception or the Mid-Level exception. It is most common for a second round pick to receive the minimum salary and be signed using the Minimum Player Salary exception. However, since the Minimum Player Salary exception limits contracts to two seasons, it is not uncommon for teams to use a portion of their Mid-Level exception in order to sign the player for three seasons. This gives the team full Bird rights at the end of the contract, and avoids the Gilbert Arenas"

Warriors would need cap room in order to sign him. Since they are deep in the tax, they don't have space. They can't use the MLE because they gave that to Nick Young.

Therefore, the only way to sign the kid was to use the minimum player exception for two years.

You are correct, we won't get his bird rights after the 2018-2019 season