If you get a message from someone you never matched with on Tinder, it's not a glitch — it's part of the app's expensive new subscription plan that it teased earlier this year, which allows "power users" to send unsolicited messages to non-matches for the small fee of $499 per month.
That landscape, in fact, is largely populated by apps owned by Tinder's parent company: as Bloomberg notes, Match Group Inc. not only owns the popular swiping app, but also Match.com, OKCupid, Hinge, and The League.
Match Group CEO Bernard Kim referred to Tinder's subscriptions as "low-hanging fruit" meant to compete with other, pricier services, though that was before this $6,000-per-year tier dropped.
They all follow that general form because the same company (Match Group) bought all of the different dating sites and changed them to the form that makes them the most money.