If it is the multi-tier wedding cake that you posted on your account, it looks like they took a round tip, piped the shape and then ran an small angled spatula or back of a small spoon through the piped buttercream to give it that indent look.
You could experiment a bit with different methods/tools on some wax paper or a cake board with your buttercream to figure out the best way to get the effect you want. Then you can scrape up the buttercream and use it again.
The only other thing I can think that it might be since the quality of the picture isn't great, is that the baker tried to do an embroidery effect with the buttercream. You can find many videos on this, but basically you pipe the edges of the swirls and then take a paintbrush to lightly dab into the inner edge of the piped buttercream and drag to the center of the swirl.
So I would probably play around with some buttercream to see what gives you the best look.
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