Who consecrates the Host? (did I say that right???)
They would have been left over from a previous Mass.
Which begs the question--sometime in 2000+ years of Church history, there must have been an occasion in which not enough host was consecrated to serve everyone--maybe during the Triduum. What happens then?
Prior to 1955, on Good Friday, only the celebrant received the Host...the one and only Host he reserved on Maundy Thursday.
Not even the pope communicated unless he was the celebrant (he often was not). The only exception was if you were dying. A priest was allowed, if necessary, to celebrate a private votive Mass of the passion on Good Friday to give communion to those near death.
Now of course in any regular Mass, if there are no more Hosts, then there are no more Hosts. No more in the tabernacle? Then the priest must merely end communion. Nothing can be done until another Mass is said.
It is not required that anyone communicate except for the celebrant. Heck, a few years ago Cardinal Rajinth decided not to distribute communion at all to any faithful at a Mass because it was outdoors, there were many people, and the weather was turning. Instead, later in the day, there were a few communion services in nearby Churches.