Two things: one, I had a similar question on the functioning of glob in a scalar context not to long ago. You may want to take a look at it Fileglob in a scalar context and More fileglob in a scalar context.

As for better ways to do it, yes you could use opendir, readdir, and grep, and while it is not relevent to this case, you should take a look at the docs for the -X file test commands as they are very useful, and for some reason, often missed by programmers new to perl.

Scott