See also lxqt/pcmanfm-qt#1523
I'm not sure if this is the right place, but considering that the sourceforge issue tracker of pcmanfm appears to be mostly dead, I'm opening the issue here.
Looking at data/archivers.list, none of the archiver integrations ensure a containing directory when extracting an archive.
For a GUI file manager like pcmanfm, (in my opinion) this is unexpected behaviour because it has the potential to pollute the current working directory. Currently, there doesn't seem to be an option in pcmanfm/libfm to configure the archiver to extract to a subdirectory by default.