Accidentally downloaded custom OS So I wanted to boot my android in recovery but instead booted into custom is download mode and instead of hitting the volume down and clicked the volume up and it started downloading something I got scared that this is gonna wipe my ROM and replace it with a custom OS so I held volumedown+homebutton+power button to escape then I booted normally into recovery and from there I booted into my android safely so should I worry that a problem will occur in the future and what does this custom OS download mode do?
Assuming you're talking about Samsung's download mode, when booted up cold, it only accepts input from a connected PC (via Odin/Heimdall), so if you haven't connected it to a PC, then you didn't even touch anything, and thus safe.