We do try to open source features that are requested by open source projects, such as the branded login page after a HN discussion https://news.ycombinator.com/item?id=10931690
I agree that falsely accusing people of looking at the EE code would be very bad. So far we only once declined a contribution to CE by claiming it was EE code, in this case the code was verbatim, the diff showed a zero character difference. Future calls will be harder but we'll try to prevent false declines.
More about this our criteria to merge CE contributions if they are already in EE can be found in https://about.gitlab.com/about/#stewardship