I have to admit being surprised by this error. I've never seen it, but there were numerous memos to the trainers to insist on correct hand position because of it. I always trained correct hand position, but for proper TL control reasons, not inadvertent TOGA. If your hand is in the correct Boeing position the thumb is over the AT disconnect switch, true, your 1st & 2nd fingers are also hovering over the TOGA switches. i.e. the correct position gives instance access to both without any hand movement. Therefore the brain has to send the signals to the correct digits depending on what you want to happen. Thus I've never understood how the correct hand position prevents wrong selection.
The incorrect hand position I observed frequently, was guys flying with their hands flat on top of the TL's & TR's and squeezing the whole fitment; either pushing the TL's forward with their palms, and sliding them back with fingers on the TR's. Not good. The TOGA switches were hidden under their hands and inaccessible without lifting the complete hand off the TL's and replacing them. The AT disconnect switches were not covered at all.
This technique of controlling TL's on finals with sweaty palms or gusty conditions was very imprecise, inaccurate & not positive control. Their hands were moving up & back to reposition depending on wanting more or less thrust.
I still fail to understand how it could cause erroneous selection of TOGA, but evidently something did. I'm just not sure this was the reason.