True, but in that case: how would you find out "via genetic testing"?People do get IVF to have their own bio kids (low sperm motility, genetic things they want to screen for, whatever else). So if the Yaniv parents were older it's more likely too they'd need fertility treatment. Miriam and Jack could still be his parents.
(Given the context, I'd assume the "family secret genetic test" stuff is bullshit, like JY's intersex nonsense).
Jon is just lying, as per usual.