According to this article
Police in Afghanistan’s northern province of Balkh say the Taliban killed a young woman for wearing tight clothing and not being accompanied by a male relative.
Speaking only of the acts and not the veracity of the article itself:
Wearing tight clothing in public and going out without a maḥram are, at worst, haram. Neither act has a prescribed punishment so they fall within the realm of disciplinary punishments [taʿzīr]. Disciplinary punishments have a maximum of 40 lashes, though fines and confinement are also possible. Even public nudity would merit no more than this. But death? Definitely not.
On the other hand: The deliberate application of lethal means to end the life of a specific individual without right (aka premeditated murder) does have a prescribed punishment: Death.
And Allah knows best.
p.s. Walking around in tight clothing without a maḥram is not evidence or proof of fornication. Not even walking down the street naked while calling out for sex is evidence or proof of fornication. Both acts from a responsible individual [mukallaf] are definitely sinful and worthy of disciplinary punishment, but no matter how suggestive of fornication those acts might seem to some: neither is evidence or proof that the individual has already engaged in fornication.