Going off of this, how do you judge letters that seemingly aren't "extremely professional?" For example, I do research right now for my ochem professor, and he's become my mentor to the point we're on a first name basis and play FIFA together with some of his grad students, know his family, etc. I can definitely see him putting somewhere in my letter something along the lines of "DrShephardWannabe is an excellent FIFA player, we've had him over for dinner, he's lighthearted and knows a work/play balance" just because that's his personality. I'm sure he would elaborate on how we got to know each other so it doesn't look like I'm just casually playing video games or dining with him, but are points like that viewed as a plus to the personal aspect of the letter, or more of "so this guy probably knew the professor beforehand and just got a letter from him"?
If it makes any difference, the man who wrote this letter is extremely renowned and probably has admission deans on speed dial, he's also wrote several letters so I'm sure he knows what to write but I'm just taking a guess because I know his lighthearted personality.