Intent data is provided by a third part (Clearbit). Its worth noting its still in beta.
Its an ‘educated guess’ as to which companies are visiting your website based on lots of signals from Clearbit like IP addresses . The data in your website visits reports is based on the accounts you have in your Hubspot account - i.e contacts that are known to belong to those accounts/companies based on their emails addresses etc.. its confirmed data.
They won’t match up perfectly unfotunately because they are different data sources.
Its worth having a quick look at the below for reference to Clearbit - Buyer Intent Data Software | HubSpot