(I also have problems with the IPA symbols.)
First at all, I never said that the letter LL is always pronounced as /j/ in every Spanish dialect, because that is not true (and, for instance, not for my dialect). The correct pronunciation of the LL is a palatal lateral approximant:http://en.wikipedia.org/wiki/Palatal_lateral_approximant
The pronunciation of the Y is a palatal:http://en.wikipedia.org/wiki/Voiced_palatal_fricative
depending on the context.
It is very usual in some areas (in Spain, for instance) that LL and Y are pronounced just as Y. And that is also true for Mexico:
"Yeísmo: Del mismo modo, no se diferencia la pronunciación de y y ll; ambas son una aproximante palatal sonora /j/ como la y del español estándar."http://es.wikipedia.org/wiki/Dialecto_mexicano#Fon.C3.A9tica_y_fonolog.C3.ADa
The only exception to these pronunciations is in the Rioplatense dialect (Uruguay and some areas of Argentina, as Buenos Aires), where Y and LL were pronounced with the sound of the French J (ZH) or, and this pronunciation is growing up among the young generations, with the sound of the English SH.
Perhaps they were pronouncing the palatal /j/ in the affricate allophone and to English ears that sounded as an English J (like when I hear the English vowels and distribute the sounds not like they really are but matching with my vocalic distribution).