It may be the secondary structure of this RNA molecule that permits the first DNA strand synthesis by the reverse transcriptase

Complex RNAs can be primed by self annealing or hairpins or any other interaction between the RNA and other nucleic acid molecules in the mix.

See when total RNA is used as template its rRNA are most stable RNA type, followed by mRNa and tRNA, however our templates are never ideal they have broken rRNA parts, which intern prime for rRNA amplification. Try doing a ribosomal clean up and then do oligoDT CDNA synthesis.. your result would be more enriched