The parts list you read is probably a variation of the one that I read years ago. Walther USA had .pdf parts lists on their sight, but they were filled with misinformation such as listing the black oxide finish as a "blue" finish, plus they got the weight wrong, (too heavy) the trigger pull weights wrong, (too light) and the dimensions were wrong, (OAL too long) presumably because they were largely copy/pasted from the specs of centerfire versions. So I contacted Walther Germany about it years ago in 2017, that's when they told me that it wasn't made of ZAMAK, but their own proprietary alloy that was much stronger.
As for the Walther Forums, well... In my experience they're kind of biased against newer production Walthers, with the overwhelming majority of users sharing the sentiment that they were junk, and thusly were happy to accept any information which backed up their opinions. Seriously, I wrote a thread there after I had spoken with Walther Germany to inform everyone of what I had been told, but it didn't fit their narrative and obviously saying that the guns were made of "pot metal" made it far easier to push that narrative, so they dismissed the words of the company itself outright and just kept right on repeating what they knew to be misinformation.
Now some folks have told me that the Forums are better since I left, but last time I checked, (about a year ago) the PPK/S .22LR (2013 to Present) Subforum was still awash with perpetuated misinformation and declarations of abysmal quality, so at the very least, the overwhelming majority still dislikes the PPK/S .22, and they're still spreading misinformation about it.
Now granted, it could all just be marketing... Maybe it is made of some proprietary variation of ZAMAK with some slightly different percentages of this or that, and maybe it's factually no better than ZAMAK, but ZAMAK has a bad rap thanks to cheapo guns like Jimenez Arms and Hi-Point who make big, clunky 9mm Pistols out of the stuff. Meanwhile, Henry Repeating Arms has made the receivers on their .22 Rifles out of the stuff forever, they just plate it with Brass. So it works fine for .22LR regardless.
Personally though, I'm willing to take Walther's word for it that the PPK/S .22 is made of a proprietary alloy of superior strength. What's more, I suspect it's more of an Aluminum Alloy than a Zinc Alloy because Zinc tends to be substantially heavier than Aluminum, closer to Steel in weight, yet the PPK/S .22 weighs a few ounces less than my Stainless Steel PPK/S in .380 ACP, despite the fact that the grip frame isn't skeletonized like my .380 PPK/S, but a big slab of metal with a magazine well. In addition, if you compare the weight of ZAMAK mouse guns like the Phonenix Arms HP22 (20oz) to the subcompact PPK/S .22, (19oz) you'll find that they're strangely close in weight, with the PPK/S coming in an ounce less, which is odd considering the substantial difference in size. If they were the same material, then the PPK/S .22 would surely weight more than the smaller HP22, not less. So I believe it to be an Aluminum Alloy, not Zinc.
However, I'm not a metallurgist, so perhaps it is a Zinc Alloy with an otherwise high percentage of Aluminum which may account for the weight differential.
