The shoes were fake

“This is the same green Converse, on her feet, that turned out to be the only clear evidence that could identify her after the shooting,” he said, before slamming his hand down on the White House podium.

https://www.wane.com/news/mcconaughey-says-uvalde-victim-could-only-be-identified-by-green-converse-sneakers/amp/

Two sources familiar with the matter said that the shoes the McConaugheys had with them in the briefing room were replicas and that the girl's family has the shoes she was wearing at the time of the shooting.

https://www.nbcnews.com/politics/white-house/uvalde-native-matthew-mcconaugheys-plea-gun-control-make-loss-lives-ma-rcna32395