That's usually how that goes yes. Abstaining is usually it's own specific vote option. Depending on the system it will also usually be counted for like a vote total to see if something gets a majority too for example. So like if something needs 2/3s voting majority to pass you'd count all three of Yeas, Nays, and Abstains to get the total for that 2/3s majority.

Whereas "Did not vote" is usually just that whoever it was did not or could not cast a vote. In this case the chart pairs "Did not" and "Could not" under the same color so that's how they seem to have done it here too. The important distinction is that these members are usually not counted for majority determination for passage of motions for example. idk specifically how the UN works here though.