Yes, there is, but maybe the plugin could handle the case where there are both WordPress and Discourse comments a bit better. The two numbers could be added together, so the above example would just return ‘2 comments’. I’m doing an update today, so I’ll try that out.
Edit: this is fixed in the latest version (1.0.2)
Note: the Discourse comments numbers are cached for 24 hours on archive pages. See the WP Discourse Plugin Tips and Tricks #howto for information on how to adjust this.