Reviewing a paper with suspiciously good results
If it's technically possible but unlikely to be correct, in my opinion the best option is to request major revisions asking for more details and results, such as evaluating the model on new datasets, providing the code and trained model to the reviewers, etc. It's good to be skeptical, but it is weird to outright reject a paper that you believe might be correct without making sure that it really is incorrect. In other words, if you submitted a paper with a surprising result, would you want the reviewers to reject it simply because they are surprised, without determining why it is wrong?

Is this an appropriate way to address such results? Should I confer with the conference editor on this and voice my concerns to them directly?

For most journal submission sites, there are comments sent to the authors, and comments for the editor only. The latter is a good place to send comments to the editor. You could also email the editor directly if the journal submission site does not provide for private comments.