Looks like the producers are showing some references to a non-canon timeline to make it more canon.
After Disney acquired the Star Wars franchise from George Lucas, a lot of things have been changed. One of the most noticeable was the arrangement of the stories. The only parts that are canon are the trilogy movies and Star Wars Rebels animated series, while the rest of the Expanded Universe will not be connected with the movies and will be in a separate timeline under the Legends line up. However, some of the producers of the ongoing Star Wars Rebels series is making use of some of the stories from the Expanded Universe and making it canon in the Star Wars timeline. And the best part, they are using some parts from the favorite Knights of the Old Republic timeline.
Some of the signs included in the episode that was aired after its season break where Princess Leia bringing supplies for the resistance in Lothal. The starships in the hologram has some resemblance to the Hammerhead class cruisers used in the Old Republic. Another key hint was the fleshing of the backstory of the Mandalorians. In the Old Republic timeline, the Mandalorian War sparked the Great Sith War. And more backstories were added as some Mandalorians, specifically the Mandalorian Protectors, are allies to the Empire and it was also mentioned that there are more Mandalorian factions scattered even during the Clone Wars. And finally, the Malachor reference is a big hint that it was an Old Republic reference. Malachor was even mentioned in the visual guide of The Force Awakens and we might possibly see Malachor in the final episodes of Rebels as it also houses an ancient Sith Temple.
It is nice to see that they are adding some of the Legends stories in the Star Wars canon timeline as it is such a waste to set these great lore aside. These were created by great writers to flesh out the backstories for the Star Wars franchise. Will we be able to see more Expanded Universe stories into the real timeline?