Sweet cream generally means heavy cream; so they could mean stabilized whipped cream icing or an all butter buttercream with heavy cream added instead of milk or water. A true butter cream rather than a decorator's buttercream. You are going to have to ask them what they mean.
Here's what we call "Sweet Cream Frosting" down here in Knoxville.
Hope this helps,
--Knox--
1 cup butter, room temperature (preferably unsalted)
1 cup plain Crisco shortening, room temperature
5 cups sifted confectioners' sugar (more if needed)
1/2 cup whipping cream (more if needed, or use 1/4 cup 18% table cream and 1/4 cup whipping cream)
2 teaspoons clear vanilla
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