Absent a previous practice of doing so … the solicitation of grievances during an organizational campaign accompanied by a promise, expressed or implied, to remedy such grievances violates the Act. … [I]t is the promise, expressed or implied, to remedy the grievances that constitutes the essence of the violation. … [T]he solicitation of grievances in the midst of a union campaign inherently constitutes an implied promise to remedy the grievances.
Deirdre O'Brien does have a "previous practice" of telling Apple employees to talk to their managers about pay and other concerns. Whether that rebuts any presumption of an illegal promise set forth by her statement to employees in that specific store that she was there to "listen" will be a question for an administrative law judge and the NLRB if an unfair labor practice charge is ultimately filed.
The takeaway for all employers is that once that union petition is filed you must tread very carefully in your communications with employees. There are specific rules as to what you can, and cannot, say. Unless all of your executives, managers, and supervisors understand these rules, you are taking a huge risk of an unfair labor practice charge and the remedies that could flow from it, including a potential bargaining order.