Of course, this could simply be an experiment. But from an outside perspective of someone with a growth mindset, this approach sounds promising. Having no coupon code takes away the friction of having to search your email for the code, or search Google and Twitter for possible codes. You know that you have a code already applied to your account, so you may also skip checking the menus of other food delivery apps.
9 Ways Behavioral Economics Can Help Increase Conversion, Retention and ROI
Ina Herlihy
40113

Smart! Totally makes sense and would likely drive conversion. Did you follow up on the test?