Question on using PCA in Elbow Method to Inform number of topics in Topic Extractor Node

Hi everyone!

I found this workflow (Learn the Elbow Method to Optimize Topic Extraction | KNIME) using the Elbow Method to automatically inform the Topic Extractor node how many topics to find. In order to do this the authors use PCA and then K-means. When configuring K-means they include absolutely all columns (words from the document vector node and the PCA dimensions identified by the PCA node). Should this include just the PCA Dimension columns? Why did they included all columns?

Many thanks!
Best Regards,