This has just happened to me recently as well, I thought that I got the exclusive content without getting any payment notification(s). So now I just have the car pass, formula drift, VIP, and welcome pack items for free. I am not sure if I should use these things…
I also barely have half of all of the cars in the car pass…
I am on the Series X and play FH5 with Game Pass and own Hot wheels.
I own FH4 Standard edition on digital and all of the dlc,
FH3 standard edition on disc with all dlc,
and FH2.
Could it be some sort of “oh you own a lot of our products, so take this for free”
No. Yes. Maybe… 
Early on, pre-release, I saw (I swear) an offer somewhere promoting Free VIP for Xbox Game Pass Ultimate members. After launch I didn’t get the VIP package but also could not find any trace of said offer.
However, since then, at least twice, maybe three times or more, I have fired up the game and had VIP enabled, at least briefly. Full access and use of the perks including clothing, cars, vouchers, and super wheelspins. Until a restart and sometimes a little longer. Then locked again but still in inventory.
I’ve wondered if someone changed their mind between promotion and launch and turned it off but in some of the hot patches and updates said switch gets accidentally turned back on until “oops, that was wrong, click” and it all goes away again until the next time.
I finally fixed the issue…
…I bought the Premium upgrade 
…hey, it was on sale !