Custer was in charge. His plan failed, and he and all the men under his direct command at the time died.
That’s about as clear an example of poor military judgment as there can be.
Especially as he was attacking and chose the fight, it wasn’t one he was forced into.
Custer’s a very interesting guy. I’ve read a couple of books about him. But nobody ever accused of being prudent or careful. He was one of the very best Union cavalry officers, but only if you wanted a wild charge rather than cool, collected planning of an attack.
I find it very difficult to think that he would have tried such an attack against a similar number of Jeb Stuart’s men. To me this indicates that he underestimated the fighting ability of the Indians, and they killed him for it.