They're probably working with remains that have gone through the 'donation to science' route. That line should be taken in the context of the entire article being about keeping your own relatives skulls not just about skulls period.
Re:You Can't Keep Your Relatives' Skulls
by _archon_ on Monday September 16, 2019 @09:31AM
(#20983812)
They may purchase previously-reduced skulls and profit on arbitrage.
Re:You Can't Keep Your Relatives' Skulls
by justinclift on Monday September 16, 2019 @02:04PM
(#20986867)
The wikipedia page shows part of their setup for reducing heads to skulls, using the beetles mentioned in the article.
If that's the case, then how do Skulls Unlimited (US based company) do their thing?
https://en.wikipedia.org/wiki/Skulls_Unlimited_International
They've been around for 30+ years, and reduce human heads to skulls.