Sharepoint labeled Attachments in Microsoft 365

I have recently received emails  via Outlook on our Co Administered MS 365 that say Sharepoint. Then I also have attachments from the same senders within the Co Administered MS 365 Outlook account that do not say they are Sharepoint.  Why are some Sharepoint and some not Sharepoint? Also, the senders say these files are from One Drive - Can Someone explain this phenomenon to me? We are unaware that we have Sharepoint -