To be honest, this is a situation where it's difficult for random online viewers to know for certain why this happened this time, so I wouldn't stress about it too much. Even the very best growers sometimes deal with buds blasting (another term for when flower buds suddenly die prematurely).
Misting the bud / spike probably didn't cause this, but I'm also of the opinion that it's not a best practice. Water droplets are one of the mechanisms by which pathogens can spread in a collection. From my perspective, it's better to focus on providing elevated humidity (let's say 50% or above) using a humidifier or other means if necessary and keep water off the flowers. Also, misting indoors is usually just a brief spike in humidity, which then quickly returns to the ambient humidity. Humidifiers keep the humidity a bit more stable and changes are less sudden.
If this is a newly acquired plant that was in bud/spike when you bought it, the change in conditions from the grower/seller to your home can sometimes be enough to cause buds and flowers to drop. That's especially true if the plant has endured the additional stress of shipping. Watering twice a week sounds appropriate, but your growing conditions and a myriad of different variables are at play, so it's hard to say with 100% certainty. Plus, watering needs can change over the course of time. If there's any chance the media and mix dried out a bit too much or that the mix is broken down leading to root damage, then those sorts of things can sometimes cause buds to blast.