It gets even more interesting. The map in the article is the one that is auto-generated by the seismic stations. These readings are checked by a seismologist. Here are the revised results over the past week.
March 5-6. So far, not much activity (as was the previous week):
Then, March 7-8:
And finally March 9-10:
Here is a composite of days 7-10:
What is so striking is, first, how the earthquakes are oriented in a straight line, roughly NNE-SSW; and second, how many of the earthquakes are below 15km (blue dots are to depth less than 15km, Green15-30km).
Earthquake swarms (translated from Greek as "barrage" in article) are not so unusual. They often follow one big earthquake (called aftershocks). In this case, however, there has not been a big quake to trigger aftershocks. You also see earthquake swarms around volcanoes, such as Santorini, in which case the trigger is the movement of magma in deeper chambers. This is not likely to be the case for west Crete. So, this swarm probably reflects a movement along a deeper fault line. Even so, it is less usual that such swarms happen so rapidly along fault lines. The seismologist quoted in the article says that the development of quakes is usually slower.
Lucky for Crete, that the energy is being released in many small quakes over several days, and over a relatively large area.
It is mentioned in the article you quote that something similar happened in February. Here is a composite map for the entire month:
As you can see, the earthquake swarm is in the same place and so probably the same cause, whatever it is.