What does this mean? Spiritual context

What does it mean when I hear chanting of mantras even though no one was chanting inside home? I went to my neighbors home and I heard someone say “ommmm” and another phrase ending in “namaha”. I left thinking they are doing their daily prayer and came back 20 mins later to find that they have been on a meeting and sending messages with time stamps. At the time I heard it. The diya wasn’t lit, pooja for the day was already done. No body in the home was doing any kind of prayers. This neighbor has their headphones on since the last two hours. Only I heard it. What does this mean?