A Strange Story from When I Worked at a Hotel

This is a strange story from when I worked at a hotel after graduating. I was working in the hotel's restaurant. Since the restaurant was only open for breakfast and dinner, we had a rule to prepare for dinner around noon. At lunchtime, my colleagues and I would clean the large restaurant hall, and it was truly vast. We each split up and cleaned quietly. However, as we were nearing the end of our cleaning, one of the cleaning ladies called out to me, saying, "Hey." She was a part-timer in charge of guest rooms, hallways, and restrooms. Our departments were different, so I didn't know her name. She recognized us as new full-time employees, but we had never spoken to each other personally. "Didn't you just call out to me? Like, 'Hey there~'?" That's what the cleaning lady asked. "Huh? No, I didn't hear anything..." "Really? I was called, 'Hey there~'..." The lady seemed to have been cleaning the restroom. On that floor, there were only two restaurant halls and one restroom. And at that time, both were closed off, and there were no customers. We hadn't heard any such voice. The matter was brushed aside, but... What on earth was that?