It's because those devices are setup for WiFi-Direct.
From a protocol point of view a Wi-Fi direct connection is established using already existing mechanisms in a number of steps:
In a first step, the two devices that are to connect directly have to find each other. This is done by sending standard Wi-Fi probe request and response frames that include the Wi-Fi direct specific generic SSID “DIRECT-” and further Wi-Fi direct capability information. A device answering with a probe response frame uses the same SSID and includes vendor specific tagged information elements to also identify itself as a Wi-Fi direct device and gives further information such as its direct mode capabilities, device type and a name in readable format that can be presented to the user.
The GO [Group Owner] starts to operate in Access Point mode, sending beacons with the negotiated SSID and a group formation bit set to 1, because the group formation has not yet been completed. The SSID is standardized to be "DIRECT-xy..." with xy being random characters/numbers and any postfix.