If you have multiple pages from the same domain appearing in Google\’s search results they will count as a single impression.
Source: folwd.com
“…impressions looks at the site, not at the URLs. So if you have a query where we show 3 URLs from your site, the old one counted that as 3 impressions, while the new one shows just 1 impression.”
This means that if you have multiple pages from the same domain appearing in Google’s search results they will count as a single impression.