It's a slightly confusing way to tell, "don't worry, no matter if you connect this output to either CMOS or TTL-level input, both will work".
At VDD=3.3V, it's guaranteed the output will be above 2.9V, which is also above 2.4V.
The numbers in that table are chose so that if you look into the respective tables for the TTL or CMOS inputs, you will see something very similar. Most users don't really think about what does that mean, what's the technology behind; they just want to see similar numbers. The output circuit is most probably better than both those values.
JW