That's (apologies to say so) SAF NS mentality. Domestic protests are routine for Thai soldiers for decades, even centuries. There's nothing tough for them. These are men who willingly signed up to be trained and prepared to fight Myanmar, Cambodia and Vietnam armies.
SAF won't be useful in a mass domestic protest like that. LKY can keep dreaming and kidding himself. The so-called call in the army in case of freak election? What's a freak election, even by his own definition? It's when PAP loses power in a GE.
If there're so many voters who vote against PAP until PAP loses power, who are most of the voters? The NSmen and their relatives. Would they vote for opposition then crush down opposition? Shoot at their own relatives and friends? I'm sure if that happens, even the generals and colonels will switch side and support the new government.
To me, LKY sounds fixatedly power addicted with this type of threat. He can remain in power as long as people vote for him. Nothing wrong with that. There's no such thing as freak just because he loses, and threatening violence if he loses is way out of line.