And for good reason. Remember that trademarks are a consumer protection policy to avoid confusion. I was certainly confused at first. If it wasn't for the "Show HN" on the title, I might still be confused. The product name is "WhatsApp for Desktop", the page includes links back to whatsapp.com for the user to find more information, pictures copied directly from whatsapp.com (itself a fairly obvious copyright violation), and the file that's downloaded is called WhatsAppSetup.exe.
It is quite reasonable to think that someone could think this was official, easily missing the fine print that clarifies.
I strongly suggest anyone releasing software on the internet familiarize themselves with the relevant laws on trademark and copyright so they can avoid mistakes like this. There is no way this could stand up to legal scrutiny. Naming your product AnotherCompany PrepositionalPhrase is not something which presents an interesting legal debate, it's an amateur mistake.
I am not a lawyer. This comment is not legal advice.