The file name in the upstream source tree is not valid UTF-8. There is probably not much a maintainer can do other than ask upstream to package the sources differently.
Repacking may by an option, but it often has other drawbacks, such as the loss of a cryptographic chain of custody.
Unlike other file names in Lintian, which are printed in UTF-8, the attached reference shows the bytes used by the file system. Unprintable characters may have been replaced.