According to wiki ”The drop rate of ranger boots is approximately 1/1,000 per slot. Each medium clue reward, a player will receive 3-5 slots of items. This makes the effective ranger boots drop rate ~1/333, 1/250, or 1/200 depending on how many items a player receives from a clue scroll.” You received three items so your chance was 1/333 which equates to 0.3%