Oh shoot! Yeah that's definitely unintended. In theory you shouldn't be able to get bombs until you find the bomb bags. But that was changed later in development after the item shops were made so I might've missed that. They should just not show up on the vendor until you have the bag. I'll add that to the list of fixes.
To answer your other question, the blue bottle is a health potion. You can't use it if your health is already full. You may also encounter a red potion that has 2 servings.