That might be from the Valentine's Day promo. It stays in your Offers, even after you redeem it. Once the promo is done, it will disappear (to be replaced by other good stuff).
Seeing the exact same on the S6. Main Google Play screen, scroll down, there's the banner. And when you view the details for a movie selection, a message is present that says "You can apply your rental reward at checkout". Doesn't look to be related to a Valentines' Day offer, but I could be wrong.
Yay! Looks like I'm about to watch a free rental of "DC Universe Original Movie - Batman vs. Robin" ** Friday Nerdity - Achievement Unlocked **
The offer itself doesn't specify Valentine's day, but I do recall this free movie rental coming out around V-day (and Google advertising it that way). If you never made use of it back then, the offer remains valid for about 3 months (I think), so that's why you can use it now. Enjoy the movie!