The last barn I was at was “full board” and that just meant that my horse had a stall, bedding, daily cleaning and feeding, etc. But when the weather was okay, he was out 24/7. He rarely came in during the winter unless there was precipitation of some sort (usually rain here, doesn’t get cold enough to snow much). Summer is when he spent the most time in because we have horrible heat and humidity and bugs and there was no shelter in his pasture. So “full board” meant whatever was best for the horse at the time. He certainly went through many a thunderstorm out in his field, tail to the driving rain, grazing away.
In terms of the OP’s situation, in hindsight it probably would have been a good idea to shoot the BO/BM a text saying, “Hey, I left Dobbin in this afternoon since it looks like it’s about to storm and you said you were planning to bring them in anyway. I hope that’s okay.” Some BO/BMs just don’t like boarders taking things into their own hands without asking/notifying them about it. The horse being in could mean more time spent cleaning stalls that evening, more hay being consumed, maybe a shift in their usual feeding/turning in routine? Once you have a routine and system in place for efficiently and effectively caring for a number of horses, sometimes even the smallest change (like a horse being inside for a couple of hours before evening feeding and turn-in) can put a kink in the works. Now they have to pick the horse’s stall again, possibly refill or top off his water, put his feed and hay in with him in there. It may not seem like much to someone who deals with ONE horse, but if you’re dealing with multiple horses, these little inconveniences add up.
So, as an owner, I understand wanting to just keep the horse in. But as someone who has worked at boarding barns, I also understand the other side.
I’ve said it before and I say it again: this is why I love self-care board.