I agree it is sun burn. The fact that some of those spots are mostly white means the plant probably will not be able to recover at those spots ie. until the plant grows enough to make those spots be part of the underside of the plant rather than the top/side you will see them.
This is a very young plant so with time it will grow out of this.
I suspect the reason Daisy asks about having it wet/water drops on the plant while it is in the sun is that some people are convinced that this can cause sun burn on plants either by boiling away the water or some kind of beam focusing/magnification. Since I have never been able to establish that this actually happens when I have had my plants wet during really sunny and hot days, I am not convinced that this is a real thing. If this was a real thing, I would expect it to be ubiquitous here where the sun and UV are almost always way stronger and higher than most other places in the US and there are still plenty of people who have sprinkler irrigation setups that frequently hit cacti and succulents.
However there are circumstances that might play into this being observed by people: chemicals and/or minerals in the water: plain tap water should not be the culprit as the water here is loaded with all sorts of salts and what not. Now I do feel that certain areas of CA definitely have very high chlorine levels in the tap water, but again not sure how that by itself would cause this. However, if the water that hit the plant contains fertilizer or pesticide, then chemical burns from water are imminently possible.
Since this is a young plant it is really not that strange for it to get sunburn just by being exposed to the sun. In all likelihood this was green/shade house grown and when it got put in that communal pot I am sure there was no regard for what side of the plant may have been facing south (for shade house plants that may not matter anyway). So any side of it exposed to more sun that it had seen before had a good chance to get sunburn. The plant should get used to it if left in the sun, but it would not be unexpected if the sunburn would get a little worse before the plant adjusted, usually the adjustment involves new growth occurring at that level of exposure, while some of the older tissue may with time become adjusted to the sun exposure levels.