Transcript(omics) terminology: cDNAs, ESTs, RNA-seq, etc
The quick answer is that you are misinterpreting ESTs. EST stands for Expressed Sequence Tag. They are obtained by collecting and sequencing any mature (i.e. poly-A) mRNAs found in a living cell. Well, it was living until the experiment was performed at any rate :).

The term EST is not applicable to sequences derived from genomic data. It only applies to expressed sequences. You do have ESTs that are derived from cDNA libraries but these are expressed cDNAs. Short reads are not ESTs because we have no information on whether that sequence is actually expressed in a living cell. 

You could apply the term to RNAseq reads (depending on the experimental procedure involved) but that is not what most people would understand by the term.

In summary, the operative term of EST is "expressed". You cannot call anything an EST if you do not have evidence that it is actively expressed in a living cell.