I am a novice baker trying to learn the ins and outs of baking and getting a great end result.

My friend had just recently tried Kumquat Cupcakery cupcakes in Brooklyn and told me how delicious they were! I looked them up and found a video of the bakery on Youtube (posted below) and noticed that the batter she uses for her red velvet and chocolate cake looks like a DENSE frosting yet the outcome seems to rise up soo much. How can a batter like this rise so much? My friend said they were delicious but I pictured a batter like this to create dense dry cupcakes but my friend said they were moist?

Any input for this curious new baker??