A one-off magenta blotch on a phone photo is most likely a processing glitch rather than a scene or lighting issue. Modern phones often combine multiple frames automatically for HDR/noise reduction, and if there was strong motion or the merge failed, the result can be strange color patches or blotchy areas.

Another possibility is that the phone mistakenly applied a filter or effect, even if you didn’t intend to use one.

Because the shots before and after were normal, this points more to a temporary software/processing error than a permanent camera hardware fault. If it only happened once, it’s probably not serious. If it starts happening repeatedly, check camera app settings for filters/effects, try restarting the phone, and test with a different camera app if possible.