This is a message of the current state of this ‘Flame detector’. It says, "[MSG: Flame detector active…], then provides the current value read, followed by another message, “[MSG:Flame detection alarm cancelled.]”.
[MSG:] : Indicates a non-queried feedback message.
Flame sensor can be disabled by using $261=0 in console
Ambient values you getting are very low so i assume you are using machine outside or in direct sunlight?
The sensor is very UV sensitive, as its its primary way to detect flame, if in direct sunlight it will give plenty of false alarms