I think you're misreading the comment you replied to. "+/- 25% of a 11M of the population having been infected" means about 25% of 11M, or 2.75M, officially infected. 22k/2.75M would imply a 0.8% fatality rate.
And with respect to the counting, it seems like the Belgian numbers more of less match the reported excess deaths in 2020 within 10% [1].
[1] https://www.medrxiv.org/content/10.1101/2021.01.27.21250604v...