Names aren't copyrighted, they're trademarked. And since:
a) Arch Linux isn't selling pacman.
b) I don't believe Namco still own a registered trademark for Pacman. And they probably don't make enough money from it for them to win a lawsuit about it (trademarks require a reasonable commercial interest in order to be protected).
So there almost certainly isn't a legal issue. IANAL.
Namco is very involved with Pacman and still involved with arcade equipment based on it. Here's something my friends at Raw Thrills just introduced a little while ago:
From what I've heard on the inside, Raw Thrills has been actively working on new Pacman games based on the original 1980 source code given to them by Namco.
TLDR: They definitely still own the trademark and they are still making money on it.
Bandai/Namco certainly do hold multiple registered trademarks on PAC-MAN, at least in Europe. They cover not just the video game side[1], but everything from kitchen appliances[2] to lotteries[3] and even beer[4].
Namco still own the trademark, they do ill-advised attempts to revive the franchise every few years. Arch Linux best defense here is that it's not in the same business, so there's no risk of confusion (trademarks aren't all-encompassing).
a) Arch Linux isn't selling pacman. b) I don't believe Namco still own a registered trademark for Pacman. And they probably don't make enough money from it for them to win a lawsuit about it (trademarks require a reasonable commercial interest in order to be protected).
So there almost certainly isn't a legal issue. IANAL.