What does it mean if bitcoin has been converted to Ethereum?

Excuse me, could you please clarify what it entails when someone mentions that Bitcoin has been converted to Ethereum? Does this signify a direct exchange of one cryptocurrency for another? Or is it a more complex process involving the use of a decentralized exchange, smart contracts, or perhaps even a token swap? I'm curious to understand the mechanics behind such a conversion and the potential implications it may have for the holders of both Bitcoin and Ethereum.