Should I have placed the host into the pyx in the Communion line?

It sounds like the gentleman was presenting you with a pyx, a container for carrying the Blessed Sacrament to the homebound. Those who carry the Blessed Sacrament to the homebound should themselves be extraordinary ministers of Holy Communion, so it is strange that you had no forewarning that an EMHC was to be given the Eucharist in a pyx. I recommend talking to the coordinator of the EMHCs to find out who this gentleman was, so that you will know to expect him in the future. You might also recommend that the EMHCs to the homebound be introduced to the rest of the EMHCs so that you and your fellow extraordinary ministers will know who is authorized to receive the Blessed Sacrament. Otherwise anyone could present a pyx to be filled and take away the Eucharist for who-knows-what purpose.