Accept friend on Snapchat means someone has added you and remained subscribed to you but you haven't added them back. They continue to follow you even when you unfriend them.
How to FAST know if someone unfriended/blocked you on Snapchat
You just haven't made it impossible for them to send you instant messages. You simply wouldn't be able to see them if you don't accept them, so you'll have to add them again. They may have tried to forward a message to you that you have not yet acknowledged.
If any Snapchat user sends you a friend request, you must accept it before you can interact. Accepting a friend request is easy. Go to Snapchat and click on the profile icon at the top left of the screen. Select Add me. Accept your friend's friend request by tapping the plus sign right next to their username.
Since you removed them, the Accept button is there so you can add them back. Accept means they still added you and accepting would add them back. If they removed you, instead of it saying Accept, it would just say Add.
