You are overthinking this. Yes you do have access to lounge access in BKI (and I've been there as a BAEC Emerald), as you pretty much do on all oneworld services (including domestically in the UK of course). I wouldn't assume priority boarding will amount to much at BKI, however. There is an Enrich check-in desk which you can use, but it's not a big airport. I think the quote is a picture of your travels rather than a rule, albeit a rule that is relevant to AAdvantage members specifically.