"That supposed to be a note that should be pulled-off to and not picked as the notation indicate, right?"

Yes!  I saw that the first time & think I regarded the pitch arc as the hammer on indication!  But looking again it's not a hammer on indication & that is what Dave plays.  Again, requesting a fix in notation.

"+ what about the missing indications of upstrokes/downstrokes in some key/hard moments I have mentioned in the previous post? Is there any reason they are omitted?"

I'm not sure what part you are referring to here.  In general, the strumming (up/down) indications we not part of the process of some earlier lessons.  Then they began to to be a standard feature, so typically are included on newer songs & course material.  If there are older lessons without them that students want included we try to go back & add them on an as needed basis.

Regarding the forum image upload issue, I've encountered it occasionally myself.  It comes & goes but I've reported it to tech admins every time.  I get that it's frustrating!