This is a great one. In my opinion, there is a continuum of confidence=>arrogance=>cockiness. I would argue that you need guys all along that continuum in your dugout but that each has to be true to themselves and if you dip too far past one end or the other you are no good to yourself or your teammates.
I also think scouting this is very judgmental and based on the scout's experience or personal way to express him/herself. There were some who thought my son didn't care or didn't work hard because he's not the guy who's going to throw his helmet when things are going poorly or scream and flex when things are going well. The coaches/scouts who don't get him think he doesn't care. The ones that get him say that "He's very smart in the box with a low pulse" and that "He's a very cerebral hitter." Luckily the second opinions are his minor league field coordinator and scouting director. And the college he committed to felt the same way about him.
By way of background, he started his senior HS season super strong. His first 4 hits in the HS season were home runs against great teams/pitchers. Three of the four HRs were considered "pre-season" games so they didn't show up in HS stats. March came around and he started struggling. His team played top tier teams and those teams were throwing their best pitchers every game. He has a very good sense of the strike zone (definitely too picky at times) and got quite a few pitcher-friendly calls against him (some absolutely absurd and verified by video by his coaches). Then he started doubting himself. It was painful. His draft stock dropped. He wasn't himself in the box. But he doesn't show emotion. There were some that thought it meant he didn't care and didn't work hard. What they didn't know (or care to know) is that he stayed in the lab. Worked with his coach. Kept lifting, putting extra time in the cages and at the end of the season he came around. Fast forward to the minors, in 101 PA, he slashed .372/.465/.535 in the Arizona league (1.000 OPS), stealing 10 bases in 10 tries and playing most inning in CF. There is still a long way to go but he believed in who he know himself to be and not what one month of play said about him.
So...for him, confidence looked like not going crazy when he went through a dry spell, staying true to who he is and what he thought his worth was even when some people in the press absolutely trashed him. It allows him to be teammate who leads by actions not words. But there are definitely a lot of people who missed on him because the misinterpreted his quiet confidence as a lack of confidence.