That's simply incorrect, it's not how economics works. For example, if I stole $2000 from you and used it to fix houses/invest it would not magically become productive income.
The comment above you is pointing out that excess income a landlord makes because people are willing to pay a premium to lease a scarce or rare good they own doesn't contribute to the rest of the economy in the same way selling a hotdog does. Ergo, unproductive income.
The reason why this is not "productive", is pretty straight forward. It's unproductive because nothing is being produced. We are selling what's already there long before humans existed.
And that those supposed authorities have been teaching absolute nonsense like loanable funds.
If you want to learn about the economy, the only useful option is to look to working market participants. Some rando at the fixed income desk has forgotten more about how the economy works than those pompous frauds.
Except the LVT premise is bullshit.
Lets say I have a house I rent out for 1800 dollars a month. About 500 dollars of that will go to taxes (income, property, etc).
Out of the rest I take 600 dollars and am in the process of fixing up two more houses that I bought from a tax sale that were made unlivable through crackhead squatters.
So that leaves me about 700 dollars more. Out of that I need to save probably about 300 dollars a month to cover costs associated with owning homes. Such as the need to replace roofs or water heaters or hire arborist to take down dying trees before they destroy my neighbor's property, etc.
Then that leaves me with 400 dollars that I reinvest in other companies. So it goes to doing thing like buying bonds, etc.
The only thing that is "unproductive" here is the money being paid to the federal governemnt to go murder brown people half way around the world.
The entire intellectual basis of this "Georgian" stuff is completely bogus. The theories about monopolies are wrong. The theories about how to solve the tragedy of the commons is wrong as well. The economic efficiency theories are wrong, etc etc etc.