I am not expert and I am sure the experts here will have the correct answer. To me, it looks like they took the tiniest writing tip and drew the lines on cake then added the pearls on top of the lines. I am just guessing. Pearls come in different sizes so you would probably ask some of the people here what size of pearls to use. I could be wrong so let's see what the others have to say!!
That looks right, but there is more buttercream in other areas too. So just use thicker lines if you want to add more pearls
I think I agree w/the others :)
AI would suggest you use royal icing to make the lines and mix the sizes of the silver pearls when adding them. Let the royal icing sit a few minutes before adding the pearls and make your pattern in sections because to do a neat job, you will have to take your time...I also love this cake. Have fun.