Draw a curved arrow mechanism, predict the product of following reaction. [2-bromobutane with KOtBu/tBuOH]. Products are cis and trans butenes. Not clear on how the cis butene was made. See image.

I followed E2, with Hofmann as major product. The only thing I recall for making cis were the multi step reactions using Lindlar's catalyst, which doesn't seem to apply here as I'm not working with an alkyne. What am I missing?enter image description here