I think it is the result of recent warmth. We had some cool weather in late November and a few frosts, so plants thought "winter is here", but they don’t seem to measure time and then the mildness of December has made them think "Spring!".
Hence all the fine, white hairs: new growth from previously dormant winter roots, and these hairs are fuelling the first stirrings of spring shoots, flowering stems ultimately, not fatter roots.
So it is not your fault and nothing to do with watering or not watering in summer. You just need to rub the hairs off, annoying extra job!