I’m not sure how, but for some reasons, std::vector<double> is being interpreted as ROOT::Internal::RDF::FillHelper::Buf_t. In the picture above, I have the cursor hover above one of the variables to show its interpreted type.
My guess is that your VS code environment has the ROOT headers in its include path, so that interpreted type is probably found somewhere from one of the RDF headers. I think it’s more a VS code problem than anything.