Who waved from my mother's flat?

Yesterday, I had an inexplicable experience during my visit to my mom's home in Belgium that has left me baffled. Every few months, I travel from Paris to see her, keeping up a tradition we've had for 17 years - she waves goodbye to me from her third floor window as I walk to the bus stop down the path outside her apartment building.

This time, after saying farewell inside, I headed out and turned to look up at the window for her familiar wave. There was my mom, smiling and waving at me, holding the curtain with one hand and gesturing with the other. I waved back, taking in all the details - her smile, the motions, everything seeming clear as day.

Yet, right after, I received a text from my mom saying she hadn't actually seen me leave and was wondering if I'd made it to the bus stop okay. She insisted she never went to the window to wave goodbye because she'd heard me talking to a neighbor in the hall and opened her door to remind me about my bus time.

However, I'm positive about what I saw in the window, and certain no one else could have been in her apartment unnoticed. My mom lives alone and doesn't host guests. I'd just been inside minutes before and it was only her there. Stranger still, there was no neighbor I spoke to in the hall, though my mom believes there was.

I'm mystified by this experience. Could my mind have imagined the whole farewell gesture somehow? Did I witness something unexplained? I wasn't under the influence of anything that could alter my perceptions.

I'm hoping to get insights from others - have you had similar occurrences of seeing something so clearly that logically couldn't have happened? I'm looking for theories or interpretations that could shed light on just what I witnessed happening at my mom's window that day.