There is critical chance for healing and critical chance for damage in parallel. You need to see the skill/CP description, it usually says if it only increases one type or both.

Generally, anything that merely says "critical chance" affects both healing and damage. And it is pretty rare to see anything that affects chance for only healing or damage. But ... you will frequently see references to "critical damage done" and "critical healing done". These refer to the bonus when you crit. That bonus starts at 150% of normal damage/healing, but can be buffed further by gear sets, skills, passives, buffs, champion points, etc. So if you see something that increases "critical healing" by 10%, your chance to crit will remain the same, but when you do crit, your critical heals will do 160% of a normal heal.

This can be a little confusing to new players, and you have to pay special attention to wording. But ESO has lots of ways to increase your chance to have a crit, and lots of ways to increase how much stronger crits are compared to normal, but they are separate stats.