Yesterday Justin posted a reel on Facebook referencing backing tracks being added to the app. “ That’s why I added hundreds of curated backing tracks to the JustinGuitar Lessons & Songs App.—they’re designed to help you feel the groove and stop stopping when you play”.
I cant find backing tracks anywhere in the app 
I haven’t seen it, but couldn’t he just have meant the backing tracks of the songs?
Not sure, to me songs and backing tracks are two entirely different things. The songs have been there for years, he suggested this was something new and specifically stated 100’s of new backing tracks.
I don’t hear him saying they are new. Could be this is just a message to encourage new people to take a subscription.
Unless things have changed (I don’t have the app anymore), the music and, for some songs, the singing you get with the songs in the app are not the original songs, but reconstructed tracks sounding a lot like the original. Some even have a different pitch compared to the original. They have been designed specifically to play over, so as backing tracks.
Justin is referring to the pla along songs.
I do not know why he calls them backing tracks only in this reel.
They are not the original songs performed by the original artists.
And they are tracks to use as a backing for playing along to.
I understand your meaning when you say your take on the phrase ‘backing tracks’ is an instrumental chord progression.
I think you need to allow that it is being used differently here by Justin.
Clickbait 