The "random link" is on a domain that the Wayback machine has back to 2001. Whereas the marketingreportoptout subdomain doesn't appear to be there at all. I could certainly imagine a compromise where somebody who doesn't have access to the main sites still manages to sneak in a plausible-sounding subdomain.
Plus the site uses a certificate that is not only issued by but also owned by Cloudflare according to its metadata. It's undistinguishable from a free tier Cloudflare cert unless you know what exactly you need to look for.
Does that mean that you don't trust subdomains by default? That seems a bit extreme/unnecessary.
I don't know that I trust anything by default. It's always a risk assessment. When I saw a kinda basic-looking site asking for my credit card number, I definitely looked at the domain, and alongcomplicatedthingineverheardof.visa.com was definitely more concerning than, say, www.visa.com.
Can't even trust myself these days, its really awful. /s