I say it's spam. I would be reluctant to accept third party links in general. Otherwise tag wikis will end up as big link directories.
The site in question seems non-commercial for now, but that doesn't mean it's not spam. It looks like a github crawler without much useful content. The disclaimer seems to indicatesindicate the users good intent - but that could also have been the intention of including it. The link seems kind of promotional.
Both tag wikis already link to their official documentationdocumentations with many exampleexamples. I see no reason to link to other external sites, unless 'Sourcegraph' is something well known and accepted in the those frameworks' communities (which I guess it's not). Should theysourcegraph link from every tag wiki to their site just because they indexed some random code snippets from github? Of course not.