Planet from another galaxy discovered

An exoplanet orbiting a star that entered our Milky Way from another galaxy has been detected by a European team of astronomers using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. The Jupiter-like planet is particularly unusual, as it is orbiting a star nearing the end of its life and could be about to be engulfed by it, giving tantalising clues about the fate of our own planetary system in the distant future.

ESO

BBC

I also posted this in a separate thread! beat me to it though!

The "Planet X" guys are going to be all over this! I'm interested in the data we can gather from observing a planet in it's final cycle; something which we have never had the capacity to do before.

So how do they know if it's from a different galaxy? Can't similar arrangements/ formations appear in our native galaxy? I don't know what to think of this. NASA or independent astronomers still to this day cannot provide us with clear details about Pluto's surface. So how did they come up with this conclusion?