Thanks for posting your concern here in the Community. I'm here to help provide some information about the downloaded transactions in QuickBooks Online (QBO).
Once you connect you account to online banking, the transaction downloaded to QBO is dependent on the data provided by your bank's website. In this case, I recommend contacting your banking institution to clarify the transactions from your personal checking account that shows on the business account.
In the meantime, you can exclude those transactions on your personal checking account by following these steps:
From the left menu, select Banking.
On the Banking page, select the For Review tab.
Select the checkboxes of the transactions to exclude.
From the Batch actions drop-down, choose ExcludeSelected.
To learn more on how to manage your bank feeds, you can always visit these articles below: