Win10 64bit, T61 - Suddenly a mere 1-fingered swipe on trackpad causes window tiling!

[Muse]

I never had seen this but for the last week almost this T61 laptop has had this peculiarity. Sometimes (don't know why it's inconsistent -- it doesn't always happen, haven't figured that out) when I place one fingertip on the trackpad and swipe it some (e.g. to send the cursor up to the top right to initiate a scroll), the maximized window I'm working on disappears and all my open apps are suddenly shown same-sized in side by side tiles, in rows. Hitting ESC returns me to where I was on the previously maximized window.

What's afoot here? Was there some Windows Update that made the change? Did I accidentally change a setting? It's happened to me over the last several days probably around 30 times. Yes, hitting ESC to fix it isn't very time consuming, but it's pretty shocking when it happens and it's distracting. I don't want this happening when i don't want it to. I never initiate window tiling, don't figure I want to start doing so. Certainly I don't want it to happen when I had no intention to do it. I don't usually try to scroll using the Trackpad. I generally use up/down keys or click on the arrows or shaded bar in the scrolling bar at the far right of a maximized window to do any scrolling on this, my laptop that I use without a mouse. Maybe my technique isn't optimal. Anyway, unintended window rearrangement is obviously silly.