Maybe the file has UTF8 characters on it? From the "read" docs (perldoc -f read):

Note the characters: depending on the status of the filehandle, either (8-bit) bytes or characters are read. By default all filehandles operate on bytes, but for example if the filehandle has been opened with the ":utf8" I/O layer (see "open", and the "open" pragma, open), the I/O will operate on UTF-8 encoded Unicode characters, not bytes. Similarly for the ":encoding" pragma: in that case pretty much any characters can be read.