The article specifies that the pictures were taken early the same month (April of this year).
You may see in the picture, near the bottom, that a fourth similar hole has already re-closed, and looking to the left, that two much smaller hole appear to have existed then re-closed. It's a grouping.
I would like to propose another possible cause: On April 1, 2018, Chinese space station Tiangong 1 came crashing to earth from a generally polar orbit. This could just be a crash site of some of its parts. You never know where when they crash in the oceans, but investigating the bottom of the area in the picture would permit confirmation - or not - of my hypothesis.