ah, i am actually on the other side of that debate. i am against tying them closed. they aren't able to "rest" if you tie them closed. the action of them opening is actually due to the tension of a ligament, so for them open is resting.
closing required a muscle action to work against the tension of that tendon.
i'm not familiar with T. squamosa as far as personal experience, but the foot on my T. crocea does not look like that. i'm thinking at some point this clam may have sustained physical damage to its byssus, perhaps someone more familiar with this particular species will chime in.
the foot on my T. crocea fills the byssal opening completely, and looks very smooth and milky. so while i can't definitively say that the foot area of your clam looks damaged, i am suspicious that it may have been.