I see. I actually saw it differently (for my specific needs).
I saw the calls as a cheap hedge to my upside SPX call delta that I am long. I figure that if we sell off to 1000 from here, I will lose about 3% on my calls less spot-vol correlation effects and these calls should triple in value. This is roughly equal.
If we rip and VIX settles below 30 I will lose the calls, but make 3%+ on my call delta less the spot-vol correlation and gamma. The 3% is higher than the amount I spent on the VIX options.
If we muddle along for the next few days, the calls will "drift" to something (hopefully 40+) and my SPX calls will do nothing.
So it seems like a good hedge for the next few days.
Why specifically the 30 line (it was more or less random and because you suggested it)
edit - clarification points: I paid in premium for the VIX options about 1% of my delta. In the downside scenario I figured the VIX would go to 50 (which is a number I honestly made up).