Summer air is less dense than winter air, so maybe......
No, but one potential explanation is that when it was parked at the dealership, the tires were "twerked" just enough to pull the rim away from the mounting surface of the tire, creating a very slow leak. Once filled, and parked with "even pressure" on the tires, the rim is sealed and doesn't leak.... I've had tires that leaked once and never leaked again, just something that can't always be explained or repaired.... Just watch it closely until you have confidence in it again.....
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS