No, it does not always mean so. The light, especially inductive, depends on some current in the wire. Position on the wire and direction of the transformer can affect the light trigger. Other things that can affect it are surrounding conditions, such as a broken or internally faulty plug or wire, or fouled, or as mentioned, lean. Something like a stuck valve might do this also
This may not be such a problem on older lights with a direct electrical hookup
I have never particularly favored a timing light as something like a miss indicator.
