quantum field theory - Is there a mistake in a QFT textbook

I tried to calculate one of the problems in the textbook Gauge Theory of Elementary Particle Physics by Ta-Pei Cheng and Ling-Fong Li. On page 248 you can find the following calculation of a loop

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Highlight, take notes, and search in the book In this edition, page numbers are just like the physical edition

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quantum field theory - Is there a mistake in a QFT textbook? - Physics Stack Exchange

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