I thought he was talking about getting 123, not trips.
But on of his points was that its not out of 999, its out of 1000 because of 000. Witch also makes it 10 ways of getting trips, not 9. So its 10/1000, witch of course simplifies to 1/100. So yeah, you're right.
But if were talking about getting 123, then its 1/1000.
The chance in getting any specific number is 1/999, oh and by the way you are forgetting about 234, 345, 456, 567, 678, 789 which is categorically similar in the way that you are thinking. im sorry i just had to be statistical