One revealing way to tell is passes attempted per game. Some option teams in the 70s threw it was few as 5-6 times per game.
Looking at RichRod WV days, with Pat White. They attempted 16, 18, then 20 passes per game, from 05-07 (their peak).
Florida with Tebow threw it 28, 24, then 26 times per game. Those numbers are just too high to describe the offense as an "option offense".
But I don't know where to draw the line on pass attempts.
If you remember 2013 Auburn, which lost to FSU in the championship game - they were really option-dive heavy. Their QB wasn't much of a passer, and they still attempted 20 passes per game.
'85 Oklahoma attempted 10 per game. Obviously an option team.
OR I could just look at where the QB ranks for carries on the team. If he's 4th, he might have run some option or just scrambled a lot because he wasn't capable of going through progressions. If he's first or 2nd, probably ran the option a lot.