I've only been through this once or twice. They might be threatened, concerned with their own drinking, in denial, etc. I have absolutely no business evaluating some else's motivations for asking me to drink, or analyzing their consumption habits unless asked explicitely to do so.
It sounds like both the friendship and your recovery are built on a solid foundation. I wouldn't worry too much about it, particularly if you went on and had a good afternoon afterward. No sense in future tripping or expending energy on something you don't KNOW to be an issue.
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