That’s right, it’s a short radio burst. No one can think of an astronomical object that could act like this, but every once in a while the radio antennas pick them up.
One hint: It can happen repeatedly from the same object. They have been picked up happening months apart or once less than a minute apart.
(Radio broadcasts are frequently beamed in a single direction by magnetic fields. My guess is that this is a beacon that is being swung around in different directions, and every once in a while it happens to point toward us. That way, it wouldn’t have to be so amazingly powerful, and it would also explain the apparent transience.)