you were probably pulled aside because the the tsa guy with the altoids deemed your clothing to be "non-form fitting".

your request to be within the line of sight of your property should have been met though, and the fact that the chair was pointed in the opposite direction implies that the supervisor in charge either:

a) has the checkpoint set up that way on purpose
b) has no idea how his checkpoint is set up
c) set up the equipment correctly, but was inadvertently moved, implying that:
d) the supervisor and/or screeners don't care that tsa's rules stipulate that all screening is done while passengers have positive visual control of all of their property

imo, your best course of action is to request a tsa comment card and mail it back to the address that's printed on the card. get the name of the person who denied you having visual control of your property, and the checkpoint location you were at. mailing these cards back, (rather than leaving them at the checkpoint), guarantees delivery to higher-ups who actually care about passenger rights/any other shortcomings at their airport.

and that whole altoid thing.... the machine probably froze and needed a reset to get the initial reading back to "0". causing another alarm, whacking the side, and kicking the thing all seem to work equally.