All of the above. Since your plant was indoors, it is not receiving full sun always, even the temperature is comfortably cooler than what it needs. So if you position them suddenly outside without protection, like any other plant it will get sunburnt. That is why you will often hear, do it slowly. Especially here in California, even our own gardens has such microclimates, one side may be more intense sun than on the other side.
But once the Plumie is truly fully awake with leaves, it can handle the heat and sun, provided you also give them ample watering. In their preferred growing areas, there is constant humidity, California for the most part, unless your location is more coastal, has very low humidity the further away you are from the shoreline. Our dry period is literally dry...unlike in other areas of the US they have humid, rainy summers.
I have seen them grow majestically in my homeland where it gets lots of typhoon weather in its equatorial humid heat conditions. The consistent thing there, the temperature is never below 70F and temps goes humid hot everyday, typical soil there is loam soil with volcanic origin so it is quite rich and also well draining.
Our California weather is way too different...just so many microclimates.
One thing that helps me understand my own garden is having a weather station. Though there are always daily weather news we see and hear updated, our actual gardens may register it differently. My area always meets or exceeds the forecast ...always a battle of extreme dryness and heat here once it comes around. On the flipside, it is hard to overwater my awakened Plumeria here during the dry period, water just dries out very fast. And I have made sure media is very gritty and well draining, so it will not sit in water.
