This is not really a bug.. i feel this should be in discussions not issues.. Anyhow.

You are attempting to play non-audio file as audio file? rom/startup.lua is normal lua program so trying to play it like audio file will lead to issues.
You can use music.madefor.cc to convert your music files to dfpwm to then play with speaker program. CC does not come with any sounds in rom folder. It is up to player to get them.