Without trying to alarm you, make sure you didn't end up with one or more quarts of Castrol Act-evo 2 stroke (you need the Act-evo 4 stroke). Unlikely, but the guy at the counter could have sold you the wrong stuff.
I am NOT familiar with this product, but a review of the Product Data Sheets and MSDS on the Castrol site does not indicate anything abnormal in what is disclosed. It looks like a synthetic blend, with typical adpack stuff. Nothing in it indicates where a sulphur smell might come from.
Usually Sulphur smell occurs in gear oils, and metal working fluids, as sulphur products are added for EP properties, but these don't normally get put in engine oils.