Doubt about penguins

The addition of the Penguins connection to Los Glaciares was suggested (Magellanic), but doubt has risen. Aren't penguins supposed to be sea birds?

They might be at Lake Argentino (source), this seems within the WHS area but I don't know it's true at all. I haven't found another source confirming this.

Anyone that has been there who can help solve this?

I am afraid that the "source" quoted is guilty of unjustifed hyperbole - Whales on Lago Argentino indeed!! I hope no one has signed up to a tour on that basis
Los Glaciares NP is totally landlocked (and indeed the Argentina/Chile frontier which forms part of its boundary was established along the Atlantic/Pacific watershed of the mountain range). Lago Argentino is actually largely outside the park boundaries.
Any penguins there would have to wear their hiking boots to get from the sea as Penguins don't fly (Emperor Penguins do walk long distances across the Antarctic ice but I think this is a bit different!) To be fair I guess the source quoted was referring to Patagonia as a whole rather than just Los Glaciares - the rest of the article ranges widely across that area.