Nah it's cool man, but no, I didn't use vectors (I have absolutely no idea how to use vectors); I drew this by hand. Paint Tool SAI is very good for smooth lines
Vectors are cool, you just use either illustrator for it, or the Pen tool in photoshop. They're great to use if you want to make prints of things like t-shirts or billboards, because they're unlimitedly sizable. Vectors usually have a very smooth appearance though, so probs where they got that from.