They may have been in town ?

How did you know that there were no people inside? :o Did the number of players say 0 on the farm list or on the list of players in the farm only list you when you entered? :o

If it was just a matter of not seeing them, or not seeing them on the map, they could have been at the edge of the farm, which does not always show up on the map, or they could have been on another side of the farm, possibly moving in the same direction you were so that you never met up... Or perhaps inside a House?

No, in town as on the farm there was no one on the map and in the player list there was no one
even if one player is in town and another on the farm, we can see each other but there was only me

That seems weird. :o Were you on the list or you didn't show up on the player list either?
Perhaps it is possible that you joined a farm right before the host left or had a disconnect and then the farm didn't unload right away...?
Or perhaps it could be that there was an update and the difference between versions had some kind of schism...?
Did you happen to get a screenshot?