“He, on the other hand, had very specific ideas he wanted to hammer home with citations at the ready.” It did seem like Steven was going for a gotchya moment, but I wouldn’t call this outside the bounds of conversation. I think it would have been helpful to hammer back that you are not familiar with the study, it doesn’t match the studies that you are more familiar with, and that you will look into said study after chatting. And then implore Steven to stop bringing it up. Another possibility is to temporarily assume it is true and then think how it affects your position.
One shouldn’t just dismiss an unknown study outright because it doesn’t align with your point of view. From an impartial observer it makes you look like you are dug into your position (doxastically closed). It should be dismissed because of bad science or due to irrelevance (as you have done now).
Just some thought on keeping live conversations productive, when presented with unknown studies.