We have very similar language in the Compare branch view which can confuses others and cause people who've meant to master into a feature, merge the other way around:
Sync: Merge master into feature branch
Sync now: Merge feature into master
When someobody syncs a branch from the '...' menu (under Branches), if their feature branch is some number of commits ahead of master, they'll be brought to Compare view.
There are two options on this screen:
Merge (this will merge master into feature)
Sync now (this will merge feature into master)
We should make it more clear which direction the merge is taking place.