Peculiar deprotonation of an alkenyl proton
Decided to convert this to an answer anyway. Disclaimer: I'm not an organic chemist (anymore), and corrections/suggestions are more than welcome.

One distinct mechanistic possibility here is that you deprotonate γ to the carbonyl, then the extended enolate reacts at the position you see, and then after that there's some tautomerisation which brings the double bond back into conjugation with the carbonyl (maybe during workup).



These are specific conditions under which you might expect deprotonation at the γ-position over the other α-position. In particular, the extended enolate resulting from this is more stable than the cross-conjugated enolate resulting from α-deprotonation, so this is called the "thermodynamic enolate". Paquette et al. use this term in the paper (J. Am. Chem. Soc. 1987, 109 (10), 3017–3024):


  Toward this end, the thermodynamic enolate of 6b was exposed to [...] 1-bromo-2-methylpropane.


I won't comment on the specifics of this reaction, but will mention that it can be very dangerous if scaled up.

If you wanted to deprotonate the other α-position, you would probably have more success with something like LDA. That deprotonation relies on chelation of the carbonyl oxygen to lithium (via a cyclic transition state*), so goes for the proton nearer to the carbonyl. That would be the "kinetic enolate".





* The six-membered chair-like transition state is widely taught, but is actually of questionable accuracy in this specific case. I think the transition state is cyclic, but is eight-membered or something like that. See e.g. slides 50 onwards of this very informative presentation from David Macmillan's group: "Lies My Sophomore Organic
Professor Told Me".