Yes collision mitigation it's turned on. However there's no road crossing etc. Must be something.
Is it possible it could actually brake? In afraid of someone slamming into me now. 40 years of driving, this is something new to worry about.
From the manual:
The system may automatically shut off and the CMBSTM indicator will come on under
certain conditions. Some examples of these conditions are listed below. Other
conditions may reduce some of the CMBSTM functions.
2 Front Sensor Camera P. 396
■ Environmental conditions
• Driving in bad weather (rain, fog, snow, etc.).
• Sudden changes between light and dark, such as an entrance or exit of a tunnel.
• There is little contrast between objects and the background.
• Driving into low sunlight (e.g., at dawn or dusk).
• Strong light is reflected onto the roadway.
• Driving in the shadows of trees, buildings, etc.
• Roadway objects or structures are misinterpreted as vehicles and pedestrians.
• Reflections on the interior of the windshield.
• Driving at night or in a dark condition such as a tunnel.
■ Roadway conditions
• Driving on a snowy or wet roadway (obscured lane marking, vehicle tracks,
reflected lights, road spray, high contrast).
• Driving on curvy, winding, or undulating roads.
• The road is hilly or the vehicle is approaching the crest of a hill.
■ Speed bumps, road work sites, train tracks, roadside objects, etc.
You drive over speed bumps, steel road plates, etc., or your vehicle approaches train
tracks or roadside objects [such as a traffic sign and guard rail] on a curve or, when
parking, stationary vehicles and walls.
The collision mitigation braking system will vibrate the steering wheel, flash BRAKE, sound an audible alert, and it may automatically brake - lightly or forcefully. (Pg 442-3 in manual)
I never use the lane keep assist. I've only experienced what you described when I've had the collision mitigation turned on.