Using 'them' instead of 'those' is a dialect form. Not all native English speakers speak the 'standard English' taught in language schools and in foreign countries, all the time. Some never do, and some only do so on formal occasions, or when (for example) being interviewed for radio or TV. This is especially true in the UK, where 'talking properly' has social prestige.
Many speakers speak, partly or fully, a dialect which can reflect social class or regional origin, or both. This is true in the UK and US.
Writers of grammar books have preached against using 'them' where standard English uses 'those' for at least 250 years. Writers of web-based grammar 'guides' still do so now.
Many persons are apt, in conversation, to put the oblique case of the personal pronouns, in the place of these and those; as, Give me them books, instead of those books. We may sometimes, find this fault even in writing.
From The Rudiments of English Grammar For the Use of Those Who Have Made Some Proficiency in the Language (Joseph Priestley, London, 1772)