Often it happens that VCs buy out companies from funds belonging to a fresh because the selling fund wants to show performance to their investors until "the big one", or move cash one from wealthy pocket to another one.
"You buy me this, next time I save you on that", etc...
"Raised $19 million Series A led by Khosla Ventures + $7 million"
"Today, Bun makes $0 in revenue."
Everything is almost public domain (MIT) and can be forked without paying a single dollar.
Questionable to claim that the technology is the real reason this was bought.
If it was an acquihire, still a lot less slimy than just offering the employees they care about a large compensation package and leaving the company behind as a husk like Amazon, Google and Microsoft have done recently.
It's an acquihire. If Anthropic is spending significant resources, or see that they will have to, to improve Bun internally already it makes a lot of sense. No nefarious undertones required.
An analogous example off the top of my head is Shopify hired Rafael Franca to work on Rails full-time.