You understand correctly! Thank you for this, a course contributor will pick it up and hopefully they will be able to edit the sentence (some(?) Greek sentences are locked in this beta version, not sure how much can be changed). Thanks again!
"That's (this is or he's) the guard that I talked to" or in higher register English "that is the guard with (to) whom I spoke". Both are correct but the latter is more elegant, and much closer to the Greek.