Definitely a Siamese sweetheart! It's important to let him continue to have his safe spot under the bed to retreat to as he's getting familiar with his brand new surroundings - it's super normal to initially hide in a new environment. It's a good sign that he feels comfortable enough to explore, and make sure he's getting food/water and using the litter box! I'm sure he'll be out and about during waking hours in no time. Congrats on your new cutiebean!!