On a CentOS 6 system without /etc/localtime or something else configured I would expect that DateTime::TimeZone::Local returns "UTC" as the time zone, like system's date:

$ date
Sat Jun 24 11:42:12 UTC 2017

However the output is:

$ perl5.24.1 -MDateTime::TimeZone::Local -e 'warn DateTime::TimeZone::Local->TimeZone()'
Cannot determine local time zone

I think as the last fallback the module can simply return "UTC". I checked other systems (Debian jessie, Debian stretch, Ubuntu 16.04, CentOS 7, FreeBSD 10.3) --- on all these systems date outputs UTC if /etc/localtime is missing.