The DayZ Launcher is incorrectly parsing the server browser protocol contained in the Steam A2S_RULES response.
It statically takes byte 36 and byte 38 to verify the ExpansionTerrain and DLC flag, which has been changed a long time ago already. The current protocol conforms to the ArmA 3 version and places the relevant flags way before that. The current approach retrieves a random letter from the mod list, depending on how the server is configured.
This results in servers using mods reporting in the launcher as requiring a DLC.