Grafana: What's the meaning of red/green dotted line?

Red meaning an alert triggered and green meaning an alert cleared. Check your alert settings for details.

I have setup a alert evaluate every 60s.
WHEN max() OF query(A,1m,now) IS ABOVE 0.002
if no data or all values are null SET STATE TO No Data
if execution error or timeout SET STATE TO Alerting.

I've check the value of the stats all are below 0.002.

I've pressed the 'Test Rule' and get the following result.
result
firing false
state ok
conditionEvals false = false
timeMs 3.897ms
logs [ [object Object], [object Object], [object Object], [object Object], [object Object], [object Object] ]

Well, I understood. The rule is base on 1 min, so, for example:
10:10:10 occurs 0.00278
10:11:01 alert show red dotted line because during 10:10:00-10:11:00 the max() value is 0.00278 which greater then 0.002.
10:12:01 alert show green dotted line because during 10:11:00-10:12:00 the max() value is below 0.002.