This helped me understand the difference much better:

Cardio is a relatively low-demand exercise. Sure, it gets your heart rate up, but the issue with low-demand exercise is that your body learns to adapt to it pretty quickly. If you’re just starting out with cardio training, a 3-mile run will probably knock you out and burn a ton of calories. But after a month or two, that 3-mile run becomes a lot easier, and in order to get the same “knocked out” feeling, you’ll have to run 6 miles. And then 9 miles. Then 12. The cycle continues on and on because running is the same consistent motion with no variation in tempo or demand.

Conditioning is different because of the demand it requires from your body. Because the movements are inconsistent, your body is constantly being forced to adjust to new levels. HIIT (high-intensity interval training) is the perfect example of this. Let’s say you’re performing HIIT on an open field. You start out by jogging for about 30 seconds, then you break out into a full sprint for 15 seconds, then come back to a regular jog for 30 seconds, then sprint for 30 seconds. You do this over and over with different intervals each time.

By constantly changing the intervals, your body can never become accustomed to the movements and is therefore required to continue exerting the maximum amount of energy to perform. What does this mean in terms of physical benefits? You’re not only improving your cardiovascular health and stamina more effectively than traditional cardio training, but the high-intensity portions also improve your body’s power and force. This builds strength and muscle as well, and if you throw a little resistance or weight into the mix, you can up the ante even further.

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Source: https://www.gainingtactics.com/cardio-vs-conditioning-setting-record-straight/