I found a slight references to African sumac (Rhus lancea) implying that the plant may cause dermatitis in sensitive individuals. Each article though is weak in explantation. I'll list what I've found and why I think its a weak connection:

Flora and Fauna News: Unfortunately, the text is not clear as to exactly why this plant *may* cause dermatitis. Even the wording is suspect - are they talking about poison sumac or are they talking about african sumac when discussing dermatitis?

Los Gatos Weekly-Times: Gardening: This article directly states that the african sumac can cause contact dermatitis similar to poison oak. The claim is that its in the same family. Yes that is true as poison oak and african sumac are in the Anacardiaceae family but so are about 600 or so other species of plants. This is commonly called the cashew family and there are only about 25 or so plants in the Anacardiaceae family which are considered irritants (i.e contain urushiol oil or other chemical compound). The article then goes on to argue that also Brazilian pepper trees cause a reaction - implying that so must it be true about African sumac. It is well know that the Brazillian Pepper Tree (Schinus terebinthifolius) causes contact dermatitis and the chemistry is easy to find (try a google search). No such documentation as to dermatitis-causing agents is readily available about the African sumac.

I wish I had a ready answer for you but there doesn't seem to be any science published online which would indicate that this plant causes dermatitis. Now many plants that we put in our gardens everday can cause contact dermatitis in sensitive individuals. It could be that you are sensitive to the African sumac or it may be that you came in contact with something else that you are sensitive to.