as amused as he was...

[pink dragon]

Hello. Could you please help me?

As amused as he was by this thought， he was even more surprised by another thought that followed on its heels.

I'm not sure about the meaning of the above sentence.
I understand that "as + adjective + as" is used to describe the same degree, such as "Bob is as tall as John".
But in this case, "as + adjective + as" is placed before the subject, at the beginning of the sentence. I've never seen this style.
And it says "even more surprised", so my guess is it is not descriving the same degree.
Then, what does this sentence mean???

[Tdol]

= even though he was amused by this thought...

[pink dragon]

Thank you very much!!!

[Tdol]

You're welcome.