What you're seeing here is the unique campaignId for each 'hourly' send of the 'Smart Send' email that was sent in HubSpot. To learn more about smart sending, you can see this Knowledge article: https://knowledge.hubspot.com/articles/kcs_article/email/how-to-send-an-email-based-on-your-contacts-time-zone
Essentially, this feature takes your entire list and splits it into the known timezone so that each recipient receives it at the same hour of their local time. In this circumstance, there is a master group id, also called an 'emailCampaignGroupId' in the API. Each hourly send has a unique campaignId so that HubSpot knows which grouping that particular contact was a part of. They then all relate back to the 'group' id. You'll know a certain campaign will have this because the 'app' is 'LocalTimeBatch'
For your particular campaign, the campaign group id was 41948376. You can see this either within the app on the email details page under 'Internal HubSpot Id', or, when you're getting individual events via /email/public/v1/events
Here's an example event that shows the unique campaignID for the 'hour', you'll find the group id under 'emailCampaignGroupId'