The past receivables of my QB Desktop, became Sales Income when I entered them as opening balances in QBO. Did I transfer them correctly?

Thanks for reaching out to us here, rjquinto. 

When you enter an opening balance for a customer in QuickBooks Online, the system will create an open invoice. The affected accounts on the invoice are Sales and Accounts Receivable.

The sales item on the opening balance is linked to a sales income account. This is why you see the figure on the sales income account. 

You can open the Transaction Journal of that invoice by following these steps:

1. Go to Sales > Customers.
2. Select the customer's name and open the invoice that says opening balance.
3. Click More located at the bottom, and choose Transaction journal.
4. In the Journal page, you will see the affected accounts 

Please see this sample screenshot for a visual guide:

To check the account linked to an item, here's how:

1. Click the Gear icon located in the upper-hand corner.
2. Select Products and services.
3. Click the Edit link of the product/service that is assigned to the opening balance.
4. You will see the account selected from the Income account drop-down menu. 
5. Click Save and close. 

I'm also adding this article for more insight about the opening balance:What to do if you didn't enter an opening balance in QuickBooks Online.

If you have any follow-up questions about the opening balance, please let me know. I'll be around to help you some more.