Unfortunately even beardies who have been together for 5 or even 6 years can suddenly turn on each other. It is best you separate them as soon as possible. It does look like a bite, and it's very likely that it is one since they are being housed together. You could do everything perfectly - providing separate basking spots, feeding them separately, having separate everything and one will always try to dominate the other. They are a very competitive species and are solitary lizards. Even though you bought them as a pair and they've been fine for a year, it really is best to separate them. If it really is a bite, although it appears to be a small sign of aggression for now it can get much much worse in a split second.