I imagine he decided he'd rather cash out his food at $65 than at $40 a week later. Say he was teching 5 000 pts per turn, * 54 turns * 7 more days, * $1800 per tech. That's $3.4b he gives up by converting (though he can now resell and make a little money from that).

3.4b / $25 in food price difference means if he had over 140m bushels or so maybe it was best to start to jump now.

this is assuming markets crash in a week but that may not be the case of course