I haven't referenced the video, but I think I can explain what's happening for you.
1. The clip in the arrangement view is the looped clip that is currently active in the session view while recording. In short, the arrangement view gives you a linear view of what is happening on all the tracks at any one moment.
For example, say you have clip #1 in a session view and it is a 4-beat loop. When you hit record and activate that clip, the arrangement view is going to keep track of how long that clip in the session view was active. Check the grid at the top of session view and you'll be able to see very thin clips being tracked there. Now, assume you run that clip for 16 measures and then deactivate it in the session view. When you switch to arrangement view, you will have a 16-measure clip on that particular track! Ableton does a clever little thing by placing a little tick mark at the top of each clip to let you know how long the ORIGINAL clip in session view was. So, that 4-beat clip in session view will be 16-measures long in arrangement view, but will have ticks every 4 beats to reference how long the clip in session view was.
2. No, they are no different in content. But depending upon how long you allow the clips in session view to run, the only difference I can think of would be the physical length of the clip itself in the arrangement, which again is related to what I just explained above.
2a. When you record from session view, OR when you click on a clip in session view, hit TAB to switch to arrangement view, and then manually place the clip you have clicked somewhere onto the same track in your arrangement.
2b. The only time a clip will differ from one view to another is if you manually alter something AFTER a recording has been made.
For example, say you recorded the 16-measure clip as explained above. Now you want to add a bit of pitch variety in your arrangement view on that track. You can click on that clip in the arrangement view, and the display at the bottom of your ableton panel will show all the notes in that clip. If you change any of the notes or rhythms or whatever, even the clip envelopes, the clip is now different from your original in the session view. This is a typical process one might use in Ableton to tweak notes or rhythms here and there to add variety, depending upon the nature of your music, of course.
