It is possible, to get a small spark when connecting the battery, especially if the battery has been out for a while. There are filter capacitors in the radio and other computers that will pull a momentary surge when being powered up. This surge lasts but a split second and then the power draw drops to nearly zero. There are some things like the clock and radio that pull a very small amount of power to maintain memory when the bike is off, but that should not be enough to make a visible spark.
It does not matter if it is the pos or neg, which ever is connected last will make the spark.