There are a couple things going on here that conspire to make a confusing picture. First, the suggestion description comes from the user's history, so, yes, it could be old; this is WAI. But when we attach the "Switch to this tab" button, it implies that this message is open now, when that precise message isn't.

The reason that it matches is because we strip hash references - text in the URL after the # - when matching, because we'd like links to further down a page, for example, to match that page. Unfortunately, Gmail (but not the only site) puts context into its hash references. In this case, clicking on an individual message adds a hash ref to the URL.

Solutions: We might not strip hash refs (but this would then not produce matches for Docs, after simply paging down, for example), or close this is as WAI (or do more extreme things like only honor hash refs on certain sites, but we don't want to maintain a changing list.) A more correct but difficult solution would be to dynamically keep track of sites whose URL changes after the user scrolls. Anyways, that's the reason why you're seeing it.

+tommycli or Justin, krb@ sums this up really well -- should we keep this as an FR, mark it for review later, or mark it WAI given GMail updates URLs frequently?

I can take this - it's a follow-on to tab switch suggestions - but I'm fine with reviewing later.

drive-by: I don't know if this matters for whatever solution you have in mind, but the history system stop paying attention to title updates of a page after a short time.  See
https://bugs.chromium.org/p/chromium/issues/detail?id=782064&desc=2#c34