You're right, M1 usually is lifting the bar between sts, but it depends on how the designer defines an increase. The pattern the user is making may give a recommendation.
When you look at the math (great to have the stitch counts at the ends of a rows), it only works if you use up a stitch to make the increase. The first row increases the sts by 50% from 12 to 18. The second row increases by ~33% from 18 to 24.
(if you lift the bar between sts you'll almost double the stitch count (11 additional sts).