Quote: "Is it through wifi only?"
Some background
"Broadcast and Run" would work via a physical LAN-cable also, IF you could connect it, using say an RJ45 jack, into your phone or tablet.
But since most phones and tablets can only use WiFi or the cellular data connection, you are basically limited to the WiFi option.
Why only the WiFi? Well, because the cellular data IP-connection won't do, because it's in a different subnet (so the broadcast packets won't reach it)!
And why doesn't the USB-connection work? Well, because it doesn't assign an IP to your device.. It's more of a "direct" connection.
So... yea, you kind of need WiFi for "Broadcast and Run" to work on your phone or tablet.
Prerequisites
The prerequisites to make "Broadcast and Run" work are (briefly), that your computer and portable device are on the same IP-subnet, because broadcasting the app to the player on the device uses "broadcast packets" which are confined to the subnet from which they originated.
On the software side, AppGameKit and the Player should be using the same version.. as in, don't broadcast from AppGameKit 108 BETA8 to a player that was made for V1076...
Since the packets are confined to the local subnet, the apps you are testing won't be starting on your neighbours devices, if they happened to be running the player on their device also.. (Well, nowadays it's rather easy to hack into anyones WiFi, but you know, barring that, you'd be fine.)
Cheers,
AgentSam