Translation:One kilometer is one thousand meters.
If you didn't have a typo, then your answer should have been accepted and is worth an error report. Numerals are supposed to be automatically accepted for numbers, but I think I read somewhere that higher numerals (100+) are not automatically accepted, so the contributors might have overlooked that they needed to enter "1000" as an acceptable alternative.
I notice only one person above uses "metre" rather than "meter". Personally, I grew up with "metre". We converted to the metric system from imperial in the 1960s. I can tell you that it was a relief, after 12" (inches) per foot, 20/- (shillings) in the pound (£) and 12d (pennies) in the shilling. Also rods, poles, perches, furlongs, chains, roods and acres. Gallons, quarts, pints. All gone forever thank god!
Dictionaries seem to disagree with you...
2: meter (US) noun
or British metre /ˈmiːtɚ/
meter (plural meters)
In Standard English, this crucially depends on whether the phrase is prenominal or not. Prenominally, the phrase will not show plural marking, while elsewhere it will have the normal plural marking, as appropriate.
- The bureau is 3 meters long.
- This is a 3-meter-long bureau. (prenominal)
The basic unit of length in the metric system; it was originally planned so that the circumference of the Earth would be measured at about forty million meters. A meter is 39.37 inches. Today, the meter is defined to be the distance light travels in 1 / 299,792,458 seconds.
- The bomb shelter has concrete walls that are three meters thick.
- The room is six meters square.
- (metre) The property lies within approximately 150 metres from the construction site but would not be directly affected.
- countable noun
A meter is a metric unit of length equal to 100 centimeters.
[US]regional note: in BRIT, use metre
She's running the 1,500 meters here.
The fly half stood alone on the right of the field, five metres in from touch.
I went to the same window and clung to an air vent ten metres above the ground.
an athlete running at 10 meters per second
(and under 'metre')
Every few metres the cat stopped and turned to look at me.
Over 3 700 square metres of office space is available.
The huge sculpture is made of 500 cubic metres of ice.
Basically, the computer can't switch the order. It would mean that it has to store the information as "一キロメートル is the proper translation of 1000 meters" which is wrong. Stick to the order the sentence is given in.
Also, you will find instances where you CAN switch things in a sentence and Duo will be fine with it (there's almost always an exception to things). The reason I don't think it should be accepted here is because of the topic particle putting the focus/emphasis on "1 kilometer". Your sentence, due to the way English works, puts that same focus on "A thousand meters" which is not faithful to the original Japanese sentence.
People from other countries have to adapt to us in certain ways. It's only fair that we adapt to them in other ways, such as this. In Japanese, it's helpful to understand the measuring system that they usually use. (Of course, there's also measuring rooms in tatami mats, which isn't exactly standardized since tatami mats come in varying sizes... So, yeah, if you're a realter moving to Japan, there's going to need to be some...adjustments.)