The given example API query does not return results from the geosearch API. It returns results from the pageimages, pageprops, coordinates, and description APIs. These are internally fed the result of the geosearch API query.

In other words, the geosearch module generates a private list of pages (not exposed here), and feeds them as a generated list of titles to each of the actually targeted APIs.

To receive page information, you need the same kind of query as for any MediaWiki API query that returns page information. We use https://www.mediawiki.org/wiki/API:Info for this.

For example:
https://en.wikipedia.org/w/api.php?action=query&formatversion=2&prop=info&inprop=url&titles=Presidio%20of%20San%20Francisco

"pages": [
    {
        "pageid": 59480,
        "ns": 0,
        "title": "Presidio of San Francisco",
        ..
        "fullurl": "https://en.wikipedia.org/wiki/Presidio_of_San_Francisco",
        "editurl": "https://en.wikipedia.org/w/index.php?title=Presidio_of_San_Francisco&action=edit",
        ..
    }
]

In other words, include at least prop=info and inprop=url in your batch query, and use fullurl from the result.

With the above in mind, I hope the following now makes sense:

@Jdlrobson

Titles returned by geosearch are non canonical.
These originate from the the query to the geosearch API.

The API query in question doesn't return results from the geosearch API.
These titles are canonical. (Afaik, none of our APIs return non-canonical titles.)
To get URLs in the API response, include inprop=url in the query, whch comes from the info API.

Change 824136 had a related patch set uploaded (by Jdlrobson; author: Jdlrobson):

[mediawiki/extensions/NearbyPages@master] Fixes: Titles returned by geosearch are non canonical

https://gerrit.wikimedia.org/r/824136

Change 824136 merged by jenkins-bot:

[mediawiki/extensions/NearbyPages@master] Fixes: Titles returned by geosearch are non canonical

https://gerrit.wikimedia.org/r/824136