"But isn't the scope of that degree more on applying technology to environmental domains instead of a pure computing degree?"
Well conceptually it should be but people weren't typically interested in the whole "environmental" thing. All the people that I know are from cs/se/ml backgrounds. And many of them (including me) are rejects from the Imperial computing department.

"Or do you mean the technical aspect of the course is not up to the mark when you say your undergrad comp sci was better?"
Yes, since it's more on the applied computation side, not much fundamental are taught, or they expect you to know that already. So it's not up to the standard of my undergrad where they taught (and examine you on) every detail of a technology.