A 2008 paper found anchoring effects from these kinds of “incidental environmental anchors”, but then a replication of one of its studies with a much larger sample size found no effect (see “9. Influence of incidental anchors on judgment (Critcher & Gilovich, 2008, Study 2)”).
So that at least says something about why the people running your forecasting workshop thought this would have an effect, and provides some entry points into the published research which someone could look into in more depth, but it still leaves it surprising/confusing that there was such a large difference.
A 2008 paper found anchoring effects from these kinds of “incidental environmental anchors”, but then a replication of one of its studies with a much larger sample size found no effect (see “9. Influence of incidental anchors on judgment (Critcher & Gilovich, 2008, Study 2)”).
So that at least says something about why the people running your forecasting workshop thought this would have an effect, and provides some entry points into the published research which someone could look into in more depth, but it still leaves it surprising/confusing that there was such a large difference.