I'd criticise you for those too.
Yes, you could have used "... FROM joined_chats jc, users u WHERE jc.user_id = u.user_id ..." but I dislike that method for several reasons.
it confuses the row selection conditions with join conditions and obfuscates the structure of the query and its table relationships.
That syntax can't be used for LEFT/RIGHT OUTER JOINS. Even if you want a cartesian join with no conditions, use tableA CROSS JOIN tableB to be explicit about what is required and you haven't just forgotten the WHERE bits.
I have found queries using WHERE JOINS run slower than the same query using explicit JOIN .. ON syntax.