I've encountered the same thing when moving into a left turn lane and slowing to a stop. Vehicles making right turns from my left toward me sometimes cause an alarm to sound. I can go months without it happening or a couple of times over a couple of days like this week. I take the irregular occurrence to be just situational happenstance--my vehicle angling left toward the turning vehicle with just the right timing with the position of the other vehicle.
The first couple of times this happened I thought it was a false positive blind spot alert since I had my left turn signal on and the alarm seemed to go off as the turning vehicle was about side-by-side. Since I'm watching the road as I come to a stop I can't say if the side mirror flashed in any of these instances. Since those early occurrences, I'm more inclined to think it's a false positive collision avoidance alert though I'm not certain.
If you were curving left toward the oncoming cycles, not right and away, I'd guess you were getting a collision avoidance alert. A lane departure audible alert, if you have that function turned on and got near a road line, shouldn't activate on a curve. I've found that to be the case without exception so far.
While simply driving, I've had a collision avoidance alert only twice, both on the same day. I was going 55-60 mph on a two lane back road with vehicles in front slowing to turn right. I could hav been just driving a little frisky that day, not being sufficiently defensive by braking to the vehicle's liking. However, there were 800 lbs. of people in the car, the only time I've been hauling that kind of weight. I doubt that's a factor, but who knows--maybe the vehicle somehow senses the weight and assesses a longer braking distance.
Anyway, these safety system false positives don't bother me much. It's the false negatives--not operating when they should--is more problematic if one is prone to trust them.