I dug around with a search engine a bit, and "sev3/sev4" refers to software support "severity level". There aren't standard definitions, but it appears that the higher the number, the lower the importance/impact of the incident, with 3 and 4 being, generally, stuff that barely matters or is merely affecting performance, without affecting accuracy or stopping the show. Sev1 would be a down server, a corrupt production database, crashed internet connection, and so on, that cause alarm bells to sound and people to run around and flap their arms and make chicken noises. Sev2 is stuff that affects production but isn't stopping the show. Sev5 appears to generally be things like a background color on the UI making something a little hard to read, or a font someone doesn't like (i.e., should be fixed, but when it's appropriate/convenient).

Which makes the question kind of odd. I'd expect an interviewer to be more interested in prevention/cure of sev1/sev2 than 3/4.

Pretty obvious that, if you have proper DR in place, like automatic failover on to a standby server, a lot of sev1 can be mitigated to 2 or even 3. That would be of interest. But handling of sev3/4? Who cares? Doesn't show anything useful about an interview candidate.

Of course, I'd add to the list sev0. That's where the whole company is shut down and goes out of business because of some system/server/farm disaster. Sev-1, where whole civilizations are destroyed by IT errors (it's gotta happen someday). Sev-2, where humanity itself is threatened by an IT mistake (Terminator, et al). Not sure whether -3 would be destruction of a planet or the whole physical universe being wiped out (LHC doing something they really didn't plan for maybe? Ice Nine?). It's completely extensible!