In duplicate, is it ethical to base your play on other people's body language?
Under no circumstances is one entitled to draw inferences from the actions of a partner or teammate.
Under certain circumstances one is entitled to draw inferences from the behavior of the opponents at one's table, on boards one is playing against them. As you note, deliberately peeking at an opponent's scores is not one of these cases.
However, under no circumstances is one entitled to draw inferences from the behaviour of opponents at other tables, about boards not currently at your table. In this instance, there additionally seems to have been a conscious interpretation of forbidden knowledge, making the violation particularly egregious.  Other than for a novice, I would likely assess average-minus on the board in question, and a further procedural penalty of one additional full board if I felt there was sufficient evidence to establish a likelihood that the egregious violation occurred, other than from lack of knowledge.
If I felt that the offender had lied in order to hide the deliberateness of the offense, that is blatant cheating. If sufficiently established I would immediately eject the player from the game, consequences to the movement not withstanding; impose a lengthy suspension from the club; and file a full incident report to the ACBL describing my actions and the evidence I used to reach the decision..