I've seen a similar photo in the past. Several years ago on Reddit, a guy posted a photo of the top of his mag catch plug in the frame of his P-07, and it was rusted to the point that it was crumbling. If I remember correctly, he worked construction on the Texas gulf coast and so would have been sweating a lot on his gun as well. Although he swore that he had tried multiple kinds of lube on it to stop the progression of the rust, but that it hadn't worked. Then in typical Reddit fashion some mod started talking about how internal parts in Glocks never rust and CZ should get into the 21st century with their metallurgy or whatever.
Personally in my P-07's I have never had any rust issues at all, not in the bore, slide, frame, nowhere. I have profusely sweated on them on some occasions, but not on a regular basis. As mentioned, if you carry IWB in the summer heat, doing yardwork or something similar, you can expect to soak your holster and your gun. If you are carrying in a leather or leather-backed hybrid holster, then it is also going to absorb a lot of that sweat. I also had this issue with a Black Arch Protos-M hybrid which has a synthetic material that is supposed to wick sweat and allow it to evaporate, but still left a puddle of absorbed sweat after a day of working in the outdoor heat. So when I carry in the heat where I will sweat profusely, I prefer to carry in a full Kydex OWB holster to avoid that. If I was using a leather holster in those conditions I'd probably treat it with Sno Seal or Obenauf's paste to partially waterproof it with beeswax, at least on the side that was against my body. That is still not a 100% solution though, with leather being so porous.
I don't carry my guns in a lubed condition I'd call "wet" because I don't want lube migrating out of the gun onto my clothing. Instead what I do is clean my guns bone dry with some combination of solvents like 99.9% isopropyl alcohol, acetone, brake cleaner, electronics cleaner, canned gun scrubber, etc. depending on whether I'm strictly cleaning metal or also exposing polymer parts. Then metal parts get treated with either Eezox or Hornady Oneshot with Dynaglide dry lube / protectant. Then friction-bearing surfaces get a small dab of Slip 2000 EWG. I've used a lot of different cleaners, lubes, CLP's, protectants, etc. over the years but these are what I finally settled on. In practice, my polymer pistol frames get wiped about 90-95% clean with patch cloths and 99.9% IPA, then they get sprayed out with electronics cleaner or gun scrubber, then sprayed out again with Hornady Oneshot which leaves behind a coat of Dynaglide dry lube and protectant, then the rails, hammer / sear interface, trigger bar contact points, etc. all get a very light dab of the Slip 2000 grease applied with small foam swabs. I don't go out of my way to lube the mag catch parts but they do get hit with the Hornady dry lube as part of the overall process. When I have my frame detail stripped I will also remove the mag catch to clean, inspect, and re-lube the spring, pin, etc. while I'm in there.
