In this example we take the muting technique a step further by adding individual finger muting techniques in our right hand. This is the key to creating clean and singing lead lines with the slide. It will be difficult in the beginning to adjust from perhaps shaving played finger style guitar using only chords, where you actually want all the notes to ring out. This is the opposite; you want to be able to mute a string as soon as you have played it, at the same time as plucking another string with another finger. If you have some experience with hybrid picking, this will come more naturally to you I think.
The second example using the thumb to pluck the D-string is a bit trickier, and I recommend you take it slow at first, and try doing this throughout the whole scale!
I also want to add, that when I mention D-Dorian, I was of course referring to A-Dorian and nothing else, slip of the tongue (and mind) there. ;)