I am not 100% sure, but I think it is one of the last big waves of acceptances. I know they keep accepting up until late July (each year, they often have one person who gets an acceptance call a few days before orientation due to someone deferring), but I think acceptances do not come out in as big of batches as the Dec, Jan, and Feb call outs. Again, I am not completely sure, but based off of activity on the SDN LLU thread last year, and the fact that most people I know got calls between Dec. and Feb, is what leads me to make this hypothesis.
Also, there is one last interview (that I know of) in late Feb, so there may possibly be call outs again later in the spring. But at this point, I think it will probably be a much smaller batch of calls.