Okay, two things here ;
i) 'about two seconds from takeoff' - does that mean they'd been going for two seconds, or, in the opiuon of the passenger they were going quite fast.
ii) In my experience whatever the reason, the reason the pax are told is similar to 'a warning light in the cockpit', unless it was something serious such as eng failiure. They are hardly likely to say 'something broke and lots of bells and lights went off' are they ???
Also, if they were really two seconds from lift off, they must have been almost at v1, very unlikely to stop for a predicative windshear (may not be enough rwy left to stop in a windshear situation).
An engine failure, would perhaps have been a little more obvious, and a config warning ( no flaps etc), would have sounded as soon as the 'epr' button is pressed (probably 2 secs after the start of the take off roll ???????).
Devils advocate is correct with the reasons to stop - so there arent many others left are there ?? I agree - it is a little puzzling what happened.