As impressive as their elaborately decorated temples were

Usually "As A as B like "as pretty as she"" denotes "A as the extent or amount of B", but this underlined means "Though their elaborately decorated temples were impressive". Is it because of the verb "were"? How can you tell the difference?

st102)Looking back, scientists have unconvered a mountain of evidence that Mayan leaders were aware for many centuries of their uncertain dependence of rainfall...As impressive as their elaborately decorated temples were, their efficient systems for collecting and warehousing water were masterpieces in design and engineering.

keannu said:

How can you tell the difference?

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The C word.

Incidentally, when the construction is is used in this way, the first 'as' is frequently omitted.

What do you mean by C word, please?

Rover_KE said:

​CONTEXT!

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I think this is one of those very rare occasions when I might not have objected to a second exclamation mark. ;-)