While you’re not wrong, it’s also possible that they simply used cracked versions.
So you’ve never once in your life bought a laptop or prebuilt PC, used or otherwise? Because if you have then you’ve paid the Windows Tax.
And again, the version of window that comes on prebuilts and laptops isn’t free, the cost is rolled into the price of the device.
The user you replied to probably build his pc from parts and thus not paid indirectly to Microsoft.