Explanation
To make sure the decision splits reflect the correct tent for each customer, Northern Trail Outfitters should use Entry Data as the type of data in the decision splits. Entry Data is thedata that is captured at the time of entry into a journey and remains static throughout the journey. Entry Data can include data from data extensions, Salesforce objects, or API events. Using Entry Data will ensure that the decision splits are based on the tent that each customer bought at the time of entry, and not affected by any subsequent purchases or data changes.
References:https://help.salesforce.com/s/articleView?id=sf.mc_jb_entry_data.htm&type=5

A contact is a person who interacts with a brand across one or more channels, such as email, mobile, web, etc.
A contact is identified by a contact key, which is usually the same as the subscriber key in Marketing Cloud or the contact or lead ID in Sales Cloud. When users register with the mobile app, they will create new contacts in Marketing Cloud with their device IDs as contact keys. However, these contacts will not be associated with their contact keys in Sales Cloud until they are synchronized through Marketing Cloud Connect, which can take up to 24 hours. Therefore, newly registered users will create additional contacts in Marketing Cloud until they are matched with their existing contacts in Sales Cloud. References: https://help.
salesforce.com/articleView?id=sf.mc_co_what_is_a_contact.htm&type=5 https://help.salesforce.com
/articleView?id=sf.mc_co_implementing_contacts_in_the_marketing_cloud.htm&type=5