^ Well here goes a little spoiler that won't really spoil anything.
Mick from Earth-X was VERY GOOD!! and Leo's best friend... so Leo misses his best friend.
We all know how our Leonard was, more evil shades of gray like our Mick...

So both Mick and Leo miss their friends. And they have the same face as their former friends but do not act the same. For Leo, he miss how his heroic friend was. Mick miss how his awesome bada$$ friend was. lol I guess he might be missing Doomsworld Leonard now.