Timezones need to be included in VEVENTs. Both DAVdroid and the other client do that.
DAVdroid uses ical4j, which includes an own set of the Olson Timezone DB (see https://github.com/ical4j/ical4j/wiki/Timezones). These timezone definitions may be different from the system definitions or the definitions other clients may use.
The ical4j (and thus DAVdroid) timezones include a time zone history (just have a look at the definition). That means if you move a DAVdroid-created event in Europe/Berlin to pre-1916, the correct local offset (+005328, local solar time offset of Berlin in those days) will be used while the event created by the other client will just stay in +0100.
And yes, that may be useless, but it’s correct and I don’t see a reason to change it, especially because it’s an ical4j thing. The only “solution” could be to use system time zone definitions, but I guess the ical4j author(s) had good reasons to include their own database, so we will probably stick with it.