This has happened to me twice. What i have realised is, most people open fiverr on both, their phones and laptops/computers.
Some of them have two different profiles open on different devices. This could be because of multiple reasons but they are the same person.
As long as the buyer does not user different accounts to haggle you or cheat you, its completely alright. Although, you can ask for a clarification from them too, that’s how i came to know about this phenomenon.