It's a mis-understanding that all .so belong to the devel package. All .so that are SYMLINKS to .so.* belong to a devel package.

*.so which are plugins do not belong to devel packages (keep in mind that they have no versioning and any abi change will result in crashes of the consumers unless rebuilt!)

in this specific case, though, the .so is indeed a symlink. The error here is that the consumer tries to dlopen the .so instead of linking the .so.* or dlopen()'ing the .so.* (it pretends to understand any ABI thrown at it)