An email alias is typically an email address that redirects to your true email address. Which is conceptually fine, but the OP hasn’t shared specifics so for all we know they used a temporary email address from a service that spammers use.

And GitHub does have a spam problem (if you haven’t dealt with it yet, consider yourself lucky). Just the other day someone opened an issue in one of my repos and in less than a minute two spam accounts replied with links to download malware. Fortunately I caught them right then and there, deleted the comments, and reported the accounts to GitHub which banned them soon after.