You are technically right, but in this forum roi often means that you got your money back (since you lose them most of the time lol).

According to wikipedia
return on investment = (gain from investment – cost of investment) / cost of investment
or
return on investment (%) = (Net profit / Investment) × 100
where:
Net profit = gross profit − expenses.

So if your cloudmining contract repaid itself, but did not generate any profit, it would be most accurate to say it was 0% roi, but it's no fun