The Red car was driving poorly for a few minutes before this clip also.
I beleive meds legal or illegal,due to time of day, a reason for driving as i couldn't see any gadgets being played with.
Common with alot of drivers to close gaps, instead of giving oneself a option in case something doe's go wrong.
I only see a few every few months on road,most are usually on phone,or drunk.( i usually ring 000 for drivers like this as there a accident waiting to happen)