Only Jedi and Sith bother to use laser-swords since kyber crystals are rare and by the time of the Empire even more rare since the Empire keeps hording them all for weapons. A practice the First Order does as well. We've seen Chewbacca and other welding on the Falcon.
Can you do the fine electronic work required to keep a starship flying with a lightsaber? Wouldn't you want something less likely to cause permanent damage if the ship gets jostled?
Asking a question like "why does a mechanic droid have a particular tool" seems to miss the whole point of an astromech. They're walking toolboxes, that's why! Seriously, how does this get to be a for page discussion? It was just a funny little bit. No need to over think it.
It's pretty clear it was a thumbs up, but for a second I also thought it was a flip-off, before I thought about it a little.