Good suggestion, Steve. I'll have to back-track again. From Brophy & Partridge, 1965:

"THUMBS UP. An expression denoting intense joy or gratification....E.g., 'Thumbs up, boys. There's buckshee rum tonight.' Also as an adjective: 'It's thumbs up in this company now the S.M.'s gone on leave.' Often accompanied by a gesture, both thumbs vertical above clenched fingers. Occasionally used with a sexual meaning."

So one *might* say he was all fingers and thumbs when he wrote the 1928 passage.

Had Brophy intended something else in 1928, he presumably would have included it in the later book (first ed. 1930). And the inclusion suggests that B & P thought "thumbs-up" notable and novel in WW1.

In my experience the interjection is rarely heard in the U.S. The gesture, of course, is universally understood. One thumb almost always suffices.

I doubt I've ever heard B & P's "thumbs-up" as an adjective, or with a specifically sexual meaning - which may have been less sexual than contextual.