The command powershell.exe -W Hidden is just a shortened way of writing powershell.exe -WindowStyle Hidden.
It just means you'll see a brief flash of the Powershell window and then the window will be hidden while it's still executing in the background.
If the command didn't have the -WindowStyle argument, you would have seen what was happening and been able to close it.
It has no bearing as far as detection goes, or any ability to really hide itself.