Increased vascularity is typically the result of two things: decreased body fat %, and increased strength training exercise volume / intensity.
If you have increased strength training volume / intensity in the period in question, then the increased vascularity you have observed would not be surprising, even if body fat % is about the same.
Actually... Increased vascularity is typically caused by an increased RBC (Red blood cell), which you do see in very high dosages of T-Resveratrol. My advice would be to back down the dosage, or start watching your blood work extremely closely. Keep in mind that most of the data in animal studies shows that very high dosages are more life limiting than anything else. It descreases your risk of cancer, but at the expense of a shorter life...
are you saying rbc count increase->vascualar appearance, not just both being caused by aerobic training?
Low BF% for vascularity is a given. Aerobic training can help to some degree due to temporary nitric dilation effect, but you can eat a handful of M&M (or any simple sugar for that matter) to get the near same effect, which is what contest bodybuilders do before a show.
Also, hardness and vascularity can be achieved by many routes. The first is to increase potassium (fluid balance change). Most androgens (DHT) will also increase vascularity as well primarily by blocking estrogen formation which increases sodium retention (Lowering estrogen levels decreases sodium retention). Androgens have the added benefit, however, of giving a muscle hardness as well. When you see extreme vascularity, however, such as what you see in bodybuilders, this is caused by increased RDC levels. In fact, the best way to visually detect a long term steroid user is by looking at the veins on their arms/hands. Because of long term increased RDC levels, you will typically see that the individuals veins will be abnormally large in diameter.