I found the following sentence printed in an ESL textbook for Korea students:
"This because people often make quick character judgements."
To me, it seems ungrammatical due to the "this because" construction. However, I can't quite figure out the rule. In certain situations, I can think of some similar constructions that could be considered grammatical. For example: "All of this because..."
This [situation - we don't know what but the context should make it clear] is because...
You're right that the original is not grammatical.
Welcome to the forums!
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.