I don't agree with this.
Eating a 700 calorie surplus would make anyone gain a lot of fat, regardless of whether the diet is clean or not. Even a surplus of 500 with a clean diet would cause fat gain.
OP, eating clean is definitely better for your health, but don't be mistaken that eating clean does not let you get away with eating a big surplus without fat gain. But yes, if you are eating 2800 cals now and maintaining then start out with a clean diet at about 3200 calories with 1.5 grams protein per pound and you should be gain some nice, slow weight. If not then 3300 to 3350 calories should do the trick. PERSONALLY I do not think You would need to get to 3500 calories or above.
If you can afford, GW should help with staving off some fat gain.