Why do Retirement Accounts Realized Gains show up in the Itemized Categories Report
Because you didn't Exclude those accounts from being included on the report and you received those Gains
IF you sell a security at a profit THEN the correct accounting for that profit IS "realized gain." What else could it be?
Even though you don't recognize realized gains (or losses) in retirement accounts, that doesn't change the fact that it IS a realized profit or loss.
I was just trying to figure out how to keep it from showing as income in my categorized income/expense account
If you want to exclude a Category from a report, click on the gear at the top right to customize the report, then on the Categories tab, un-check that Category.
The Category for Realized Gain is _RlzdGain and by default it is hidden, so you may have to check the Show hidden box to see it. Hidden Categories are shown in (parentheses) in the list.
If you want to exclude all the transactions from retirement accounts, un-check those accounts on the Accounts tab.