Ok..so there are numerous known geothermal spots inside Katla's caldera that are known as cauldrons.
What they are saying in the article below is that the area where these quakes are occuring, is not one of them. Hence they basically have no idea what exactly is going on.
Also..they say that this spot within the caldera is a part of Múlakvísl river so they would expect flooding to the east of Katla.

[link to www.mbl.is]