That's likely it. Weirdly, turning off that feature may not make all that much of a difference, bc it's so incredibly rare, but if you don't need it - like a long press of the power button would do just as well, in the also rare event that you want to turn it off at all - then disabling that feature would give you peace of mind.

Either way, I'm glad I could help by giving you the idea of how to (maybe) fix it!:-)

The frequency of this issue happening probably varies per person like depending on pockets and usage patterns and such. Like nowadays when I go cycling I either put the phone into an attachment on the front of the bike, or after that broke I put it in my backpack, and either way it never randomly turned off. And in my old Nexus where the issue did happen, the headphone jack working to pull the phone up more than it would have done all on its own probably contributed. i.e., for some people it will never be a problem with their patterns, but if it is for you, then presuming that's it, disabling that power-off feature (if you can) should make you much more satisfied!:-)