No one can argue if they make a vague statement, although there is nothing wrong with asking for clarification when the plans are made. A weekend is a span of 2-3 days and very generic, so I always ask for clarification. I don't think logically with AS, a 'weekend' is an exact enough date for us
Example:
Them: Let's go swimming next weekend?
Me: How about Sunday the 19th?
Them: Oh, I meant the weekend after that, I am out of town this weekend.
Me: Ok, the 25th?
The start of the week to me is Monday, some calendars don't start with Sunday on the left, but start on Monday depending on your country usually.
If the day is Monday, 'next weekend' is never 'this weekend', however, if it is Sunday, and still the weekend, then 'next weekend' is five days away. I've never understood 'next weekend' to be 'this weekend', unless you are 'in the weekend'.