Can guest network be hidden?

Not without also hiding the "main" or "private" network.

You have two options......

1) Leave both the "private" and "guest" network visible

2) Hide both the "private" and "guest" network

Hiding a network is mostly an illusion though, since there are any number of free utilities available on the Internet that will reveal a hidden network in seconds. So, anyone who really wants to see your network(s) can do so very easily, and very quickly.

Did you change the name of the guest network, then hide it? If you did not change the name of the network, then devices will remember a network to which they have previously connected.

The same way that you would get them to forget any other network that the device has joined in the past.

On a Mac......open System Preferences (gear icon on the dock)

Open Network

Click on WiFi on the left panel to highlight it

Click Advanced at the lower right of the window

Here you will see a list of networks to which the computer has connected in the past.

Click on the name of a network that you want to forget to highlight it

Click the - (minus) button at the bottom of the list

Do the same for other networks that you want to delete

Click OK, then click Apply in the next window that appears

Restart the Mac

If the device is an iPhone or iPad, you will have to log onto the network that you want to forget

Tap Settings on the home screen

Tap WiFi

Tap on the blue "i" next to the name of the network

Tap Forget This Network