Did you ask a sacristan? That’s the person to ask.
Sometimes they would be there so people can put a host into a pyx and place it on the table with the rest of the gifts for offertory, so Father can consecrate the hosts going to the sick directly in the pyx for each extraordinary minister for the sick and doesn’t have to do a transfer, but there are other possibilities.
Had there been more hosts than that, I would say it is possible that a low attendance is expected and the faithful who intend to receive Holy Communion each drop a host into the ciborium that will be taken up at the offertory, but the sacristan usually puts out more than two dozen hosts in that case. When there are only two dozen people or fewer, the sacristan can just as easily count heads. Having said that, you’d know if the number left out might have easily covered the number expected for that Mass. (A sacristan typically puts in a few extra, in case someone receives who doesn’t know “the system” or someone comes in after offertory but receives Holy Communion anyway.)
No, those hosts could not have been consecrated. Once consecrated, hosts are always either in Father’s line of sight, in the tabernacle, or on the person of someone who has the office of taking Holy Communion to the sick. The Blessed Sacrament would never be left unattended or unsecured.