This is too ambiguous to actually be seen as Sam questioning Steve's legacy. It can mean a lot of things that have nothing to do with Steve but has something to do with a black man carrying a shield that was owned by Captain America.
When did this happen? A lot of things contributed in Sam reclaiming that shield and Sarah was the least influencer in him coming to that decision. I don't know where you're getting this.
Since I didn't see it i'm not going to waste my time thinking about something that is not canon.