libgit2 would often not provide quite the same topological sorting as git, since there are multiple possible topological sortings which are all correct.
A recent PR ported over more code from git to make the output more consistent for other reasons, so you make use of that. Specifying both a topological and time-based sort (
GIT_SORT_TOPOLOGICAL | GIT_SORT_TIME), equivalent to
--date-order will sort the tips you requested by time with the current