"They are eating rice."
Well the reason is because, when people say, "Ta men chi fan," It translates more as, "They are eating food," or "They eat." In the same sense, "chi fan le ma?" Translates to, "Have you eaten?" It's an old cultural language point because Chinese ate mostly rice back in the day. Other foods were present, but 90% or more was rice. The phrase just stayed around. If you say, Ta men zai chi fan, we know 100% that they are doing the action of eating rice.
饭 is word for meal, and culturally, all Chinese meals consisted of mainly rice. Honestly, if Duo cared about the content of the meal, they ought to have at least given the full phrase 米饭 Other 饭 words: 午饭 (wǔfàn; lunch)，饭碗 (fànwǎn; rice bowl also figure of speech about livelihood)，饭局 (fànjú; dinner party)
The correct translation for "they are eating rice" would be, "Xianzai Ta men chi fan". This translates literally to, "Currently, they are eating rice". Zai alone could be correct and understandable but just weaker as it could be read as, "They are at eating rice". Please forgive me for lacking tones
I don’t know why this answer has received so many downvotes.. He’s correct.
There are so many ways to say it: 我们在吃饭。 我们正在吃饭。 我们正在吃饭呢。 我们正吃饭呢。 我们在吃饭呢。 我们正在吃着饭呢。 我们正吃着饭呢。 我们吃饭呢。 。。 the structure is Subj. + 正在 / 正 / 在 + Verb + 呢 At least one of the above needs to be in the sentence to not change the meaning. E.g. you can omit 呢 and 正 and it will still retain the same meaning. if it’s a separable verb (verb+object) like "吃饭" you can include 着 in between: 吃着饭