Coran gets actually more thieving skill points total than Imoen (+48 for higher dex and racial bonuses surpass the 40 skill points granted for 2 levels). There are options to handle thievery until then like Montaron, Shar-Teel, Safana or Imoen before dualclassing.

Cheated stats.

Starting to warm up to Imoen Mage/Thief. But that because of Durlag's Tower (Underground). Seems more like BG2 than BG1. What a great dungeon. Swear I can hear Irenicus laughing the in the dark.

Not really. He could just have found a stat raising tome before meeting you. (Shouldn't be too difficult considering how easily you can get 10 of them during the game.)

Get real. The stats are illegal. They start illegal. Don't try to defend them.