They didn't lie. They always stop short of saying that masks don't work. They said that it is not a substitute for distancing (true), that health workers should be prioritized (true), that masks don't provide the expected level of protection when not properly fit (true), etc...
It is a bit misleading, sure, but no lies, they let secondary sources lie for them. So about misleading the public, I think we can say it is the case.
Now about "killing people". Did they kill or did they save people? Remember that people fought about toilet paper, even though there was no real shortage and it is just a comfort item (protip: you can wash your ass in the shower).
With masks, there was a real shortage, and it is an essential item for health care workers. We couldn't let nobodies stockpile hundreds of masks while people who are supposed to treat you get sick. That would really have killed people. And despite downplaying the importance of masks, is was still a mess.
I know a pharmacist who got tasked with supplying masks to health care workers who had masks "disappear" in transit, and health care didn't get their masks. Herself should have got N95 masks, but she didn't, instead only having surgical masks, and she had to keep them longer than recommended. She also had to deal with hysterical customers who "needed a mask" for no good reason. And it was as the importance of masks was downplayed. I don't want to imagine what would have happened if it wasn't.
Saying they didn't lie but that they misled the public is really nitpicky. They betrayed the trust that people had in their opinion. Maybe it was worth it to manipulate people "for their own good" but I doubt it.
The advice about masks was on their website on March 2020 largely because they were worried about mass public buying of masks, leaving a shortage for frontline medical workers (https://www.reuters.com/article/us-health-coronavirus-who/ma...).
The guidance was updated as more evidence came in and production of masks scaled up. This should not be compared to outright quackery.