Why when I add a song to the play next queue does it seem to add the entire play list?
This is consistent with the way many other media players work.
If you want just the one track, use its context menu via the “...” button and select Play Now, Play Next or Add to End of Queue.
Second why if you clear the queue does it stop play the song that is playing at the time?
Sonos plays tracks from the queue. No queue; no playback.
If you want to remove a single track from the queue, display the queue, hit “Edit” and change the queue contents.
You can thank the legacy iTunes users for this situation. The early iTunes devices used a “play from here” strategy that was similar to starting play from an actual CD player. Regardless of the starting track, a CD player will continue to play tracks until the end of the disc. The early SONOS default action would add a single track to the Queue. Apple users almost started a revolt over this “absolutely illogical” way of playing albums and building Playlists. SONOS finally relented and moved to a “play from here” strategy. There were cheers from iTunes fans. Very early in the life of iTunes (before SONOS was a company) I briefly had my hands on an iTunes player and bumped into this strategy. It was so illogical to me that this was the only time I have used iTunes.
Anyway, it is still possible to add a single track from your library to the Queue, but it requires a little more work. Go to the three dots belonging to the track in question and open its action list.