Thank you.I agree with Edinburgher, though something that is 'a thing' may not be fashionable. It may simply be a recognized activity or something people do.
Here are some examples from current media.
New study says sleep texting is a thing — and 72 percent of those who do it don't remember
Yahoo Lifestyle-Dec 3, 2018
'Salad Fingers' was viral before viral was a thing—and it's returning
The Daily Dot-Nov 30, 2018
Exactly. "... is a thing" is a slangy way of saying that something legitimately exists.For me, "a thing" is quite different in meaning from "the thing."
Bubble art is a thing = Bubble art actually exists.
Bubble art is the thing = Bubble art is the latest fad.
Yes, well, they have it wrong. It seems that Bubble Art is an independent producer of cultural content: radio, video, shows, etc. based in Villeurbanne, Lyon. https://www.bubble-art-prod.com/contact.
While a company is a "thing" in the "a noun is a thing" sense, it's not a "thing" in the sense meant by "Baby gender reveal parties are a thing."