If you're unsure about a particular transaction inside of QuickBooks Online, the first place to check is the transaction's audit log.
From the transaction itself (in QuickBooks), simply click on "More" at the bottom of the modal. From there, click on the audit history. You'll see a list of all edits to the transaction as well as the person responsible.
AE Tip™: Items synced from Novi AMS to QuickBooks Online will show the person's name who last enabled the sync.