EA was definitely founded by reasonably orthodox utilitarian philosophers, like Peter Singer, Peter Unger, Toby Ord, and William MacAskill.

Formal EA organizations and conferences also have a lot of utilitarians heavily involved.

So I think it's fair to say that EA is rooted in utilitarianism, although those same utilitarians might say, for utilitarian reasons, that it's a good thing when people think carefully -- or at all! -- about how to be more effective and have a higher impact, regardless of what metaethical views (if any) those people subscribe to.