if the altar has not been consecrated, anyone can go in.
in my 'home' church, i went into the 'altar' area while the building was being renovated; before it was used for any liturgies.
so if it was a new building, people would go into the 'altar' before it was used for Holy Communion.
also if the church is renting a building, only the little box (i forget the name) for the Body and Blood of Jesus is consecrated, and this rests on a normal unconsecrated table in an unconsecrated building.
so people can go in to the area where the unconsecrated table is afterwards, after the little box is removed and the things used in the liturgy (cloths, plate and cup etc.) are put away.
maybe this is what happened?
even so, it would be a bit unusual as people would instinctively feel like not going there (unless they are deacons). but it would not be wrong.