If you had simply forgotten to include the depth measurement I would see that as being somewhat abrupt or rude.
If you had asked them to estimate depth then it doesn't seem as rude, perhaps just rather direct as others have said. Basically they're saying they don't want to be held liable for any mistakes of judgement. Granted it could have been worded in a better way.
If they don't seem happy to discuss options then are they going to be happy to alter the final product (at your cost) if it turns out to be not exactly as you though?
Perhaps they've just had to deal with too many customers who think they are always right lol
