From my understanding, DDos attacks don't breach data or leak information as the are only intended to overload the servers.
The data breach certainly just wasn't a Dddos but a planned hack through BitcoinTalk’s ISP provider (that's what I know and I could be wrong )
Not due to it but during that time there was a hack and I remember theymos was giving some reward to identify the hacker.
Bitcoin Talk: In May 2015, the Bitcoin forum Bitcoin Talk was hacked and over 500k unique email addresses were exposed. The attack led to the exposure of a raft of personal data including usernames, email and IP addresses, genders, birth dates, security questions and MD5 hashes of their answers plus hashes of the passwords themselves.
Compromised data: Dates of birth, Email addresses, Genders, IP addresses, Passwords, Security questions and answers, Usernames, Website activity
Source: https://haveibeenpwned.com/