Beeping sound and then one car on visualization turned red?

[MrFusion]

Situation: Stopped at light, light turns green and everybody starts moving slowly. The car in front of me started to switch over one lane to the right, but when they were about 1/3 across the line they came back into my lane. It seems like as soon as this happened my car gave me the triple beeping sound and then the other car changed from the usual gray to a red color on the visualization and remained red even after we started moving and they were fully back in my lane. Is the red marking just to alert me as to what I should watch out for? This is the first time I've seen that happen.

 

[Petermcg]

This is the standard warning about a vehicle you are likely to hit without taking action.