Since this blip seems to have happened somewhere near the direction of the super giant red star Betelgeuse and Betelgeuse has been very dim lately it's not too much of a stretch to conclude it’s something happening there. Betelgeuse is 640 lights years away. This is relatively close to Earth and minor gravity bumps could actually be detected here.
Giant stars like Betelgeuse are like an onion in the way light elements are fused into heavier ones. This is because deeper down you have more pressure and heat. Some elements which might not fuse near the surface, like carbon , will be lit up deeper down.
My theory is what we saw was Betelgeuse starting up a new layer in the core. Since the star dimmed that means it must of contracted which would heat everything up and add to the pressure in the core. That in turn would push the core past the point where a heavier element could be detonated. Perhaps it was not hot enough to make silicon from nitrogen and now it can. Such an event would spread quickly because the new fusion reaction now provides the heat to spread this new reaction throughout the core. With all this mass slashing around from this chain reaction you get that blip but the star does not explode because it’s merely shifting into a new equilibrium.
In the image above notice how it says 'last day' . That is because once the core starts making iron it's no longer generating heat. In fact it is now using up energy to make iron or any element heavier than that. Obviously you can't maintain the balance between gravity pushing down and heat pushing up if it's now gravity pushing down and cooling contracting down. That collapse is what causes the rebound shock wave which detonates the whole star into a supernova.