You don't need to correct something everyone already knows is an exaggeration (and I agree it doesn't seem very socially aware to do so) but this is a political discussion on the internet, so

1. Everyone does not know the original figure is an exaggeration, especially by how much
2. Providing the actual information ads value to the conversation and in this context this is more important than whether the commenter comes off as smarmy or socially inept

What if they said "Hey I know you're being hyperbolic, but for anyone who's interested, here's the number estimated by experts..."?
The only difference here is tone.
 

I'm not sure why they only shared numbers for minke whales, as these don't seem to be hunted anymore in Iceland in contrast to fin whales, whom the article was about.

Global fin whale population was estimated in 2018 by IUCN to have been around 100000.
https://www.iucnredlist.org/species/2478/50349982#population