The difference between a junior SRE and a dev is that during an outage the dev will take responsibility for their own code only[1]

While the SRE will follow the problem to the next layer or component and try understand what is going wrong there even though they never heard of the system 10 minutes ago.

[1] "I know I'm on call for this team but the guy who sits next to me wrote that code" is something I've heard way too many times.

Fair.