I've gone through a few mass gain cycles. I always gain a good deal of weight the first week. I feel it's something next to impossible to gain 5# of muscle in a week, but you're likely taking in a great deal more solids than you usually are, which could account for some weight gain. Also, I wouldn't sweat the ratios or food intake. For weight gain of any sort, you have to take in more calories than you're expending.
If you do gain a little fat in the process, so? You're clearly a lean guy naturally, and you've got some specific goals of mass and strength gains. The extra weight certainly won't hurt, and I'm sure you'll lean back out once you switch off mass gain.
Lastly, no matter how much I eat, my weight gain stops after about 4 weeks. Maybe you'll see something similar.