[lsb]

globbing expression expand to all the files that match.

if a directory has 1.txt, 2.txt, and 3.txt then << rm * >> expands to "rm 1.txt 2.txt 3.txt" and is then executed.

if you have -@, 1.txt, 2.txt, and 3.txt, that expands to << rm -@ 1.txt 2.txt 3.txt >>, and that can't execute.

(if you really wanted to remove your -@ you'd do << rm -- * >> because a double-dash signals the end of command-line options.)