I think something was lost in translation there.
Your friend will no doubt be a mandatory member of the Krankenversicherung der Rentner (KVdR), see here.
However, with his income constellation, the advantage of being a mandatory member of the KvdR doesn't really make a difference.
A mandatory member (= Pflichtmitglied) of the KVdR pays:
2.6% (2.35% if he had a child) Pflegeversicherung on all income on which he also pays public health insurance 7.3% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on his public pension (= on what Deutsche RV pays out + on any public pension worldwide) for public health insurance 14.6% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on pensions paid out by the Architektenversorgung, see here. It was just 7.3% until 2003, but they changed the law. 14.6% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on any company pensions. Please take note that any pension to which an employer contributed at all is considered a company pension. So yes, this includes betriebliche Altersversorgung (bAV) pensions. Even lump payouts from betriebliche Altersversorgung (bAV) pension contracts are spread over 10 years and you have to pay public health&nursing contributions on that lump_payout/120 every month for the next 10 years.
A voluntary member (= freiwilliges Mitglied) of the KVdR pays:
2.6% (2.35% if he had a child) Pflegeversicherung on all income on which he also pays public health insurance 7.3% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on his public pension (= on what Deutsche RV pays out + on any public pension worldwide) for public health insurance 14.6% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on pensions paid out by the Architektenversorgung, see here. It was just 7.3% until 2003, but they changed the law. 14.6% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on any company pensions. Please take note that any pension to which an employer contributed at all is considered a company pension. So yes, this includes betriebliche Altersversorgung (bAV) pensions. Even lump payouts from betriebliche Altersversorgung (bAV) pension contracts are spread over 10 years and you have to pay public health&nursing contributions on that lump_payout/120 every month for the next 10 years. 14% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on any Riester or Rürup pensions 14% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on any private pensions 14% + Zusatzbeitrag (TK has a 0.8% Zusatzbeitrag) on any other income, worldwide (interest, rental income, and so on)
I assume that your friend like most architects only contributed to Deutsche RV early in life, and then changed to the Architektenversorgung. In that case his German public pension is very low, and his advantage to being a mandatory member is just paying a lower contribution on his anyway low public pension, and no contribution on his private pension.
So, in that case he would have to contribute as a mandatory member of public health insurance:
2.6% (or 2,35% if he had a child) of all the below income for Pflegeversicherung 8.1% on his public pension (= on what Deutsche RV pays out + on any public pension worldwide) for public health insurance 15.4% on his pension paid out by the Architektenversorgung, see here. 15.4% on any company pensions. Please take note that any pension to which an employer contributed at all is considered a company pension. So yes, this includes betriebliche Altersversorgung (bAV) pensions. Even lump payouts from betriebliche Altersversorgung (bAV) pension contracts are spread over 10 years and you have to pay public health&nursing contributions on that lump_payout/120 every month for the next 10 years.
I suggest that you do the above calculation with his specific amounts and check whether his result is above the maximum amount for public health&nursing insurance of (I assumed that he doesn't have a child): Beitragsbemessungsgrenze (in 2015: 4,125€) * (14.6% + Zusatzbeitrag + 2.6%) = 4,125€ * 18% = 742.50€
If it is, then he will only have to pay that maximum amount, 742.50€, and he will be correct in his conclusion that he has to pay that much because "he's going to be earning too much money in retirement".
Taken from Finanztest 4/2015: