Bash would have been more appropriate, yes. I don't think the author of the script even thought it was going to be run by users, but some debian package checker probably flagged ruby as a dependency and there it was.
A script that is compatible with POSIX Bourne shell (/bin/sh) would be more appropriate. FreeBSD, for example, does not come pre-installed with bash. If you want cross-platform portability, this is a better default.