+1

Most drivers are not expecting someone (bike, car, horse, anything) to appear beside them like that.

Never assume the driver is going straight, signal or not.

Hang back, or be sure to be in front (ie where the driver can see you).

Perhaps the timing caught your friend out with not enough time to get in front, but yes - you could have done something different. The few seconds saved by filtering through are not worth the risk in many situations.