It is a bit vague what your problem is, because you only tell what you did and what happened, but not what you expected to happen.
Also you fail to tell which version of openSUSE you use.
So what follows is based on assumptions!
You installed some boinc packages (from the standard OSS repo I assume) and after that there was a user boinc created that was set to nologin.
But I asswume that you already had a user boinc and that thus the installation has overwritten this user’s properties.
Now either there must be some mentioning of this user in the boinc documentation (which would mean that either explicitly or implicitly you are warned not to have a user boinc on your system prior to installing these packages), or it is a complete surprise even after thourough study of the documentation.
In the last case, I would say this is a documentation bug and should be reported as such to the boinc people.