The link is not wrong. If you visit the source ad, you'll discover the HTTPS link to our Meta page is correct.
I believe you've misunderstood the URL. It's in two parts:
This is the first part. It's automatically created by Stack Exchange. We have no control over it. It's only purpose is to invoke the Community Ad server. This is required, at least, to ensure that community ad links are being properly used (without 6 votes, they're not supposed to show up or be usable). I do not know why Stack Exchange does not use the HTTPS protocol for this.
The second part is this:
As you can see, it uses the HTTPS protocol as assigned in the source community ad. This is the query that's being sent to the Community Ads server. I don't know what the second parameter (
s) refers to, but it's likely some form of session ID.
The issue doesn't involve just this one ad. If you hover over any community ad, you'll find the first part of the URL to be the same (other than the numbers, which point to the unique community advertisement).
Insofar as I know, since Stack Exchange is automatically producing the URL you're indicating, it's normal. If you have a concern, you'll need to post it at Meta.StackExchange.com where the developers will see it.