Translation:He put his bag on the floor on entering the house.
We do not say "on entering" in American English. We might say "when entering"; we might say "upon entering" (and "upon is quite close to "on" - really it's the equivalent, but it's more likely to be used at the beginning of the sentence, as in "Upon entering, he put down his bag. )
Behind the curtains, Duolingo entered a dictionary of synonyms and a list of acceptable typos which can combine and produce irrelevant results.
"Ground" is a synonym of "floor". In the US, "floor" (as in "2nd floor") can also be "storey" and "storey" is accepted as "story". This is how "ground" can become "story".
The acronym at the beginning of your question was not needed.
Duolingo has implemented a list of acceptable typos and synonyms. As a consequence:
- "par terre" can translate to "on the floor/ground"
- "floor" can be synonymous with "storey"
- "storey" is also a typo for "story".
This is how "par terre" can become "on the story".
This was reported years ago.