I don't get it. Can you explain?

Edit (literally 10 seconds after submitting my comment): is the problem that a literal reading of this would suggest that even if more than one creature is caught in the cone, only one takes the damage?

On a tangenty note, this is one of the reasons I find board games and TTRPGs super fun: DnD 5e has a lot of these kinds of problems (which is why there's so many sage advice clarifications), but even in more precisely written games, the interplay between Rules as Written (RAW) and Rules as Intended (RAI) is super interesting, because we have no direct way of accessing RAI. Even when the games designers chip in with clarifications, as with Sage Advice, all that does is give us more RAW to interpret. All we can do is guess at the RAI, which sometimes means actively ignoring the RAW.

It's also cool to see how that tension manifests from the game design angle. I have a couple of friends who have either made board games, or written TTRPG books. Whether you're the reader or the writer, the one constant is that words are slippery and unreliable, so there will always be a gap between RAW and RAI