Its upto the brand and model of tv if the usb stays powered or not. A tv turned off by remote isn't truly off its in standby, it has to be in a state to accept the remote on command. Only truly way to have a tv off is to unplug it from the wall.
And to add, most modern TV's don't even have a deep sleep mode anymore, or most users do not enable it. In deep sleep, only the remote will wake it up. Most TV's just go into idle and are still Internet connected and similar. Depending on the TV, that can be quite alot of power. My 2010 TV uses only 0.17W in deep sleep, but around 15W in normal standby (manual calls it DAM - Data Acquisition Mode) and 125W when on.
I doubt the LED light will still on if the TV is turned off from the wall plug. The light might still be on if you switch it off using a remote, the TV is technically still on standby and can still power the USB LED light. Check out https://dynamo-led-displays.co.uk/ For more information