IMO, it may either refer to:
- a t-shirt which brought good luck to the soccer star (who gave it away as a present or donated it, for example), or
- a t-shirt that the player threw to the people watching the match after scoring a goal and the fan was lucky enough to grab before anyone else did.
Of course, it may also say, as you suggest, that the t-shirt in question was manufactured/sold by the clothing brand. But since you said you were quoting from a headline, I feel inclined to doubt about this last option.
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