(1) You shouldn’t judge someone until you know what they are really like.
<The Farlex Grammar Book>

(2) You shouldn’t judge anyone until you know what they are really like.

What's the difference between these two sentences?

I suppose:

(a) The speaker of (1) was having in mind one indefinite or particular person at the time of speaking.

(b) (2) suggests "any person, without exception".

 

Your understanding is correct.

[Edited to fix a humiliating blunder. I can't believe I did that!]

 

Thank you very much, AS.

[Your understanding is correct.]