Could it be merely a matter of someone simply forgetting to sign the document? The owner of the bidded project has to right to waive and formalities.
If the EC had a bid bond then seems they took the time to get one. If they were low, then they can either take the project of reject it and surrender the bid bond, which is usually 5% of the bid.
Hardly ever have I seen an owner take a bid bond, but I have a time or two.