Yes, thats birdshot.
If you see 4BK or 00BK, thats buckshot. As Dave said, buckshots dont come in packages of 25. They do have packages up to 15rds, which are the winchester buckshot/slugs.
If there is no "bk,buck or buckshot" on the box, its birdshot. From the sounds of the amount of rounds, that without a doubt is birdshot. If you're not in an apartment and have distance from neighbors, I'd think about upgrading to 00bk. I only buy 00bk/slugs for my 12ga.