Since you have a 32 bit machine, download
this file,
not this file. You want the one
without the "x86_64" part in its name.
There's a very specific reason why the 32 bit version of the Sigil installer doesn't have "x86" in its name (which it should), but the Linux 32 bit version does: the reason is that someone who doesn't know what "x86_64" means will just pick the "plain" filename.
Linux people OTOH are expected to know the difference (if they don't, what on God's green earth are they doing running Linux?).