There are many woeful technical errors, especially towards the end of this proof, but the overall strategy looks sound and can be repaired. Honestly, it feels like someone wrote down a sketch and then invited random first-year students to fill in the details with wishful thinking. I think it hardly speaks well for ProofWiki.
One of the principal ingredients is $M(n) = o(n)$, which is itself equivalent to PNT. The proof of this that ProofWiki provides is egregious. It makes the baffling claim that $$\text{“Clearly}\displaystyle \sum_{n \le N} \frac{\mu(n)}{n} \ge \sum_{n\le N} \frac{\mu(n)}{N},”$$
which is not clear to any sane reader. It's actually false at around $N = 18500$ or so.
Nevertheless, I expect one can deduce this by doing a legitimate partial summation from the convergence of $\sum \mu(n)/n$, which is proved on a separate page (this part does at least imitate the complex analysis content of Newman's proof, but I haven't looked at the details).
With this powerful result in hand, it isn't that hard to obtain PNT by elementary methods (Dirichlet hyperbola). One should be careful to choose a cutoff adapted to the implied rate of decay of $o(n)$, but I think it does go through. It just happens that the ProofWiki argument relies on enough typographic miracles that it's "not even wrong": it strikes me as little better than the old saw $$\displaystyle\frac{\sin(x)}{n} = 6.$$