Hey worms, it all comes down to your genetics really as to whether a six pack is inevitable or not. In most cases it is definitely not inevitable, especially if you are trying to gain strength. Weight gain is necessary for strength gain and part of weight gain is fat gain. Literally the only way someone can gain strength/muscle and lose fat at the same time is if they are taking anabolic steroids, which of course is bad for you.
The eating of "healthy food" has very little effect on muscle and fat composition of your body. By fat the most important factor in weight gain or loss is macronutrients i.e. protein, fat and carbohydrates, all of which are the only sources of calories/energy.
As for your experience with lifting weights, picking up 10 pounds and gaining a six pack, 3 months is a short time and 10 pounds isn't much. It would have been better if you ate even more, then you might have picked up more strength. Regardless, either you are genetically gifted or you took anabolic steroids. Rest assured, your experience is not the norm
I'm not saying that having a six pack (i.e. low body fat percentage) is inherently vain. I'm saying that the pursuit of a six pack for the sake of aesthetics is vain. As I said, in order to excel at anything which requires a high weight to strength ratio, fat becomes a liability and needs to be shed. In such cases a low body fat percentage is inevitable. I can imagine fat being a liability in soccer.
I'm glad you've been increasing your strength though and of course it will have a big impact on your sport. The most import exercise you could do is squats with the form explained in Starting Strength. It increases the strength of the entirety of your lower body which of course has massive benefits. Also the hormonal response it produces has an effect on the development of your entire body. Squats is even better for the posterior chain than deadlifts because it works your glutes and hamstrings as well is your back. Deadlifts works these too, but not nearly as much. Don't get me wrong, deadlifts are great. Just do them both! Power cleans are also an amazing exercise. They will teach you to utilize explosive power in the legs allowing you more speed and higher jumping capability.
I will just recommend to everyone that they follow Starting Strength though. Especially with your genetic gifts, it would be a waste for you not to do it.