I think the cinematography in the three scenes (classroom, the Eaton/Musgrove meeting, and Indy's House) is the best in the film -- and it's the only thing that I can tender in support of my theory that the apple snatch was planned and intentional. [Bear with me on this, I'm no film student and I'm not up on the proper terminology, and, as per usual, I go on too long.]
Watch the three scenes and check out the angles and camarawork and how each actor's movements tie into everything perfectly. From Marcus turning his head to check out the female student in the hall outside the classroom (I assume Elliot being a dirty old man would be the 'simplest' explanation there, right Finn?), to the shot of Marcus sitting on the arm of the couch/chair in Indy's house, where his figure ties perfectly into a line with the bust against the back wall, the standing lamp and Indy packing his suitcase. In this later shot, both Marcus walking into the room and the line created by him sitting on the couch arm, creates depth -- which enhances the dramatic effect when Indy tosses his S&W forward into the suitcase (this is my favorite shot in the film). The last quick shot of the gun resting in the bag positions the viewer's eye perfectly for the next shot of the seaplane.
Now back to the apple snatch in the classroom, it's in the lower part of the screen. That shot is designed to go back further into room where Indy goes to pick up the little artifacts to justify his ticket the Marrakesh. At the beginning of the shot, Marcus takes the apple, polishes it and then pockets it. As the shot tracks back into the room, Marcus then picks up the Egyptian brush (some help here from the archaelogy crowd?) and then back to Indy where he takes the proffered trinket. At this point, at the far side of the room, Indy learns he's got to go see the Military Intelligence guys, he then goes forward out of the classroom in a slight tizzy ('What am I, in trouble?'). The viewer is first pulled into the scene (helped along by Marcus's movements) and then shot out along with Indy.
I think that all the dialogue and exposition in these scenes is not boring in large part because of this great attention to detail. Even at the most dialogue intensive part of the three scenes -- where Indy and Marcus explain the Ark's history, there's the highly skeptical Major Eaton' with his bulging eyes in the middle of the back-and-forth. Not only is it's hilarious and a neat little change-up but his prescenes grounds the back-and-forth.
These scenes have a big responsibility: there has to be closure on Indy's failed attempt to get the Idol, establish Indy as an archaelogist, and set up for the major story. All this has to be done in as little time as possible without the viewers getting bored -- which is almost sure to happen when there's too much talking with actors standing around with their hands at their sides (watch a bad action movie -- like Phantom Menace or Attack of the Clones -- and you'll be surprise at how much standing around and talking there is).
Now I don't know if the apple snatch was planned, but I'd say that the apple was a visual marker that served to focus the viewer's eye in the lower front corner of the screen so that the viewer would then be pulled back into the room. Marcus's movements help move the viewer's eye along. And again, I'd argue that the apple snatch (along with Marcus checking out the female student) is non-verbal exposition that gets bonus points because it not only helps the movement in the shot but it tells us something about the character.