"Duh" questions are appropriate, it turns out. I should've checked some of the above, before posting.
I'd erroneously assumed "high end boutique guitar shop" tech would've sufficiently tightened tuners.
Upon checking, they definitely seemed loose.
Made the same mistake of assuming he'd stretched strings, but, nope.
For the past two years, I've only played acoustic, so I'm used to playing medium gauge acoustic strings.
This may explain why I broke two strings while stretching them. I do have a question:
Is it possible to push strings out of tune even with locking tuners ?
I happened to have a set of NYXL 10's so I put them on. Didn't break any of them while stretching. We'll see what happens.
Hopefully the 10's will render all of the above moot.
Thanks