Discount Code useable even though buyer is not subscribed and/or logged-in

[WCFOODSUPPLY]

Hello,

So I made a discount code for new subscribers. Paired with an email sign-up form and automated shopify email marketing algorithm, everything works seamlessly.

However, when I tried checking out without logging-in (to make an account) and without subscribing (to get the discount), I was still able to use the discount code by manually typing it in (during check out). I specifically set that code to be applicable to "email subscribers" customer segment only. There should have been an error prompt or something, right? How is it I'm able to reach up to the payment gateway (meaning the discount code was acknowledged and thus deducted from the total bill), one click away from actually paying?

Hoping for your expert opinion. Cheers!

[WCFOODSUPPLY]

UPDATE: I tried using another browser, and it "solved" my concern. Maybe, even though I logged out, my website still picked up the log-in details enabling the codes to work on checkout (since it's the same browser).