I'm afraid that if it was a tile exercise, it's not something we can control. The tiles included in the exercise are picked randomly from the best translations, so it could be any of them.
I think this one popped up because the Greek sentence for the word is Φέτος, not Αυτός ο χρόνος. So technically, that's the word you should learn. You might've seen it somewhere in the lesson, before that exercise as well. ._.
Nope, I can corroborate what "der_Guenni" reported is correct. In the very first appearance, Duo asks to select one of three possibilities: "Νύχτας" - "Φέτος" (I thought it meant fetus) and "Ημερολογίων", in that order. I had no clue so I looked first in Google Translate. I was surprised when my "fetus" turned into "this year."
What's the difference between "φέτος" and "αυτός ο χρόνος"? If I got it right, then the following should be true: 1. "This year" as subject: "this year is good = αυτός ο χρόνος είναι καλός", but not "=φέτος είναι καλός". 2. "This year" as temporal adverb: "we have good weather this year = έχουμε καλό καιρό φέτος" (Can one also say "έχουμε καλό καιρό σε αυτό το χρόνο"?)
φέτος means "(in) this year" -- it's one word, a bit like "today" is one word meaning "on this day".
αυτό το φέτος would be (grammatically, not in meaning) a bit like "on this today".
If you don't want to use the single-word expression φέτος, you can say αυτός ο χρόνος for "this year" -- or, if you prefer the slightly more archaic word, αυτό το έτος.
But αυτό το φέτος is nonsense.
What you may have heard was: ""Αυτόν τον χρόνο" which is also accepted. But you could have learned that if you had read the other commnets on thispage.
TIPS TO MAKE LEARNING EASIER and EFFECTIVE + HOW TO REPORT A PROBLEM
And check out the Greek Forum here with more links.