I've literally never seen mention of this on blind. I see jokes about leaving and then returning at L+1, but never "forcing promo" via a competing offer.
I know someone who did it, but that was a few years ago during the peak of talent competition with Facebook. And the person was clearly qualified for the promo anyway.
It's unlikely the promo was because of the competing offer. During that time with Facebook they gave generous retention grants though.
The promo process is fairly opaque, so there's no way someone would know if the committee or manager took a competing offer into account or if they "forced it".
It seems more likely they were qualified and the timing was coincidental with the competing offer.
