Even IMDb don't call themself full reliable:
Given the sheer volume and the nature of the information we list, occasional mistakes are inevitable and, when spotted/reported, they are promptly verified and fixed. That's why we welcome corrections and submissions. Our service is provided for the information of users only.
From the same IMDb link
While we actively gather information from and verify items with studios and filmmakers, the bulk of our information is submitted by people in the industry and visitors like you!
I have myself found lots of inaccuracies in IMDb, from the synopsis, wrong images, and what not
But in the case of Lupin, it's partial information. They're supposed to be 10 episodes released in part1 and part 2, 5 episodes each. Somehow IMDb listed it as 7 but as you can see episodes 6 and 7 don't even have any information as it's not even released. Even if you select the year 2021 on IMDb they will show only 5 episodes list.
Even on Netflix, it's written as 1 part and present with 5 episodes. Also, there is no release date for Part 2 yet. But if they take the path of Unsolved Mysteries then the second part may come in 2021 only.