Your link doesn't say Zelensky didn't believe it. In fact here he is a week before predicting Russia's build up would mean invasion likely. Because it wasn't just US intel showing the activity by Russia
https://www.washingtonpost.com/outlook/2022/01/20/ukraine-russia-zelensky-interview/
https://www.washingtonpost.com/outlook/2022/01/20/ukraine-russia-zelensky-interview/
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Things are more nuanced than Western liberal "tankie" blanket labels.
Here's Oleksiy Danilov in January 2022 also doubting an invasion on the grounds of costs.