Curious how much ventilation you have and if you also measured the humidity in the coop on that night?
So my coop has ventilation through the top area (space between the roof and walls). I keep it 100 percent open all summer, but only 25% in the winter. Still allows for airflow, but limits how much cold air can get in. Roosting bars sit well below these so draft is not a concern. Local farmer said a cold winter draft can really cause problems, so I was sure to account for this when I constructed my second hen house. I did at one point use a digital thermostat (got in on
amazon for like $30) and my humidity was low..30%. The University of Georgia has excellent articles on proper humidity in the poultry environment, and I'll link it for everybody if they'd like to read it. (It is written for industrial poultry facilities, but the information can totally be applied to the backyard flock.)
High humidity is a concern not just because of frostbite, but really because of ammonia levels. Chicken waste has a ton of different gases and a poorly ventilated area can severely lower air quality, let alone cause frostbite on the birds. I've always wanted excellent ventilation for both of these reasons, but some people tend to overstate what proper ventilation is because they don't experiment much. Believe it or not, you can lower the windows to minimize the amount of cold air coming into the coop without stopping proper ventilation. Humidity levels of 60+ are a serious concern, and it isn't a bad idea to invest in a meter to measure these. If you haven't, then its really hard to talk about proper humidity without having an estimate of where your coop is at. It doesn't need to be as low as you can get it, just low enough to prevent frostbite and poor air quality.
Glad to hear you are from NJ Waddles99. I'm Passaic County, probably not terribly far from where you are. Given that we experience the same conditions in the winter, I will let you know that I rarely used vaseline. The only birds I did use vaseline on were those that had very large combs (for example, my Minorca has a massive comb that is beat red, so I feel the need to protect it more). My RIR and Buff Orpingtons are cold weather breeds, so I really let them care for themselves. I will let you know that I have never had a bird get frostbite. The tips of the combs do slightly yellow on some birds, but that is because they get extremely dry (like my hands)! The air can be very dry in winter, and this can cause combs to look pale and shriveled at times. It isn't anything to be very concerned with. Large yellow segments are black tips are the indications of actual frostbite, in which case you need to take some action to protect combs and reduce humidity. I will have you know that I have not done anything to my birds so far this year, and I really don't plan to use vaseline in the coming weeks.
Link to article on ventilation and humidity:
https://www.poultryventilation.com/tips/vol24/n2