I have a Galaxy Note 10.1 tablet of a similar age, and just opened its camera app (possibly the first time ever: who on Earth would ever use a tablet as a camera?) and found the option in there. It was damned convoluted to get to: open the camera, touch a little gear icon which gave me a list of icons which included another gear icon, touch that and I get a box with 3 icons at the top (camera, video camera and, yes, another gear icon!), touch this third gear icon and scroll down, and hidden at the bottom was a "storage" option, which could be set to "device" or "memory card".
I don't know whether your S5 has better organised settings than that, but this is a Samsung device of about the same age and the option was in the Camera app's settings, just buried very deep and then hidden off the bottom of a list and off the screen. So I expect the option is also in your Camera app's settings, but if my tablet was anything to judge by it may be well hidden!
(There's a reason people criticised Samsung's UI design for most of the decade!).
As for calling it /sdcard, I'm afraid it's all due to not wanting to break backward compatibility with badly coded apps. So we need to blame either legacy app developers or Google for pandering to them. On the earliest Androids /data was internal storage (for apps and their internal data) and /sdcard was the SD card (for media and user files). Then some manufacturers started putting more significant amounts of storage into their phones: 4 GB, 8 GB, even 16 GB. And they wanted the phone to be usable without an SD card, but many apps were written to read/write data to the card. So the "solution" was to partition the storage, allowing 500 MB, 1 GB, even 2 GB for apps (/data) and the rest for media and user files, and so that everything would work seamlessly they called that second internal partition /sdcard. Then they needed to give a different label to the actual SD card (which often differed between manufacturers). Actual SD card naming has got more standard, and /data and /sdcard are no longer physically distinct partitions but virtual volumes, but somehow Google has never bitten the bullet and said "this naming is stupid, and you should all have migrated to more sensible file paths we've provided by now, so as of the next major release we're changing /sdcard to mean /sdcard (or getting rid of it altogether) and if your app no longer works that's your problem. You've had 6 years to update now and that's long enough".