Genome assembly, de-novo, less query coverage

Question

[chullijoby]

Dear Sir/Madam,

I have single end data (Ion Torrent) and de novo assembly performed with MIRA (660 contigs) and SPADES (753 contigs). I just blasted few contigs it showed very less query coverage (17% of 63000 bp) and comparatively less identity (81%). Also performed reference assembly. Only 3% of the total reads aligned to the reference genome.

1. Why query coverage is very less?
2. Why less identity?

Thanks and Regards