Nope, it was Lululemon, they were all making sporting apparel which you could wear while working out, but were nowhere close to the fabric, design, and style that Lululemon had, and they were completely clueless and neglecting the women's market.
They eventually realized and have IMO caught on ( UA and Nike have great lines which have great fabrics, but am a guy, if you ask my wife she will go with Athleta, which is lower priced than Lululemon, but is comparable in a lot of aspects).
Athleisure was born in Europe in the 80s (shell suits). But lululemon has like 5 shops in total in the continent (Amsterdam, Paris, Zurich, Frankfurt, Berlin).
And what exactly “gym clothes” is? Shorts and a sleeveles shirt? People wear that 50 years ago outside gym. Or someone branded their particular contemporary design as “gym clothes” and pushes that? In my gym, people wear different kinds of shorts and t-shirts, mostly by nike, adidas etc, and they wear similar stuff outside. I wasn’t even aware that there is such fashion movement as “gym casual” that is distinct from “sport casual”, and I thought I was fairly fashion aware (for a guy). But i guess that Europe is now behind the trend in this matter...
Seen hundreds of girls wearing the style in the streets of Madrid and London. Granted London has ONE Lululemon store AFAIK, but it has hundreds of other brands doing the same thing too, so I doubt they set the trend.
Am a guy and buy mostly UA ( their quality is kickass and they fit well). But people swear by Lululemon's quality and its ability to hold up well. IMO they've managed to become Patagonia-like, in gaining a cult-like following.
Pretty sure that was Nike, Adidas, and Puma.