I think that very probably, since the OP mentions going back ‘to the choir’, and since in many parishes the default position, especially with teens at Mass, is that ‘at communion everybody comes forward, and just cross your arms if you are not able to receive’; and I can see somebody who has just probably exhausted himself or herself coming to Mass to sing with the choir, probably having taken some strong cough medicine before Mass, maybe in an overheated church, just kind of shuffling along in a fog, distracted by also perhaps things that he or she needed to be doing for school, a report due, various family responsibilities, etc., and so in a moment of auto pilot response just automatically imitating the gesture of the person ahead of him and absent-mindedly consuming the Host.
Right now my nearly 90-year old mom, normally sharp as a tack, is recovering from a garden variety cold (thank you, great-grandson), and she managed to shuffle down and put her phone charger in the refrigerator because she had put the rest of her lunch in there and just on auto pilot did the same thing with the phone charger. Sometimes when one is not feeling well, strange things happen!!