Zereh, I would consider your version a poppyseed cupcake. I home bake a lot, but don't have as much experience (commercial and home baking) as many on this forum. Personally I would think that a muffin is more dense than a cupcake or cake. Though some muffins are "lighter", I still think they are different from cake.
example: I tried making a banana cake. I wanted to recreate something I used to be able to buy and can no longer get. I took a banana bread recipe and used that as cake (with one slight modification) and it definitely was still banana bread. I eventually found a banana cake recipe that's really good. I have yet to sit down and compare the two recipes but definitely will soon.