Happy to help here! I haven't seen these particular values myself before but can take a stab at helping you investigate. 'Other campaigns' usually means that the traffic came from a custom campaign, the drilldown 1 is the campaign name and drilldown 2 is the source/medium.
Do you have any campaigns set up in HubSpot?
Also can you provide any more info on how these contacts were created?
For instant support you can always reach out to HubSpot support. If not, let's figure it out here 🙂