No. It just means spammers have correctly guessed your email address. They send emails to millions of auto generated addresses in the hope that some will be real addresses and not bounce back, thereby confirming it is real.
Forward the spam as an attachment to firstname.lastname@example.org for Apple to deal with and update their spam filters.
I disagree as this spam also came to an alias of my mac.com email address and this is a pretty unusual and weired combination of characters combined with underscore and such. I also disagree for the reasons that my wife has received spam the same day and her last name is nothing you would guess or come across running a nice randomizer.
There is something going on which is beyond brute force guessing and I'd like to know, what!
I agree with Russellmilne
I'm totally confused about the iCloud email thing myself. I've never used or given this address to anyone. And then last week I got an email there from someone I know (haven't asked her why/how she used it, she probably doesn't even know) and today a SPAM email to that account. Weird! I poked around and didn't see a way to shut the door to that account, for now I'm just going to ignore it, too many issues that I need to solve!