Dangerous is the first word, probably forced on then used “wobble nuts” to get them bolted up to the hub, obviously an MOT failure with just 4 nuts fitted so straight insurance accident rejection.
Another method is to use hub adaptors which bolt onto the hub with the correct 114.3 PCD and the wheel studs are at 120 to enable the wheels to fit correctly but again iffy.
The wheel bore on Lexus IS generally 60.1mm (the size of the hole in the middle of the wheel which fits over the hub centre). If the BMW wheels have a larger bore you can fit spigot rings to reduce it to the correct diameter but I doubt this is the case with this car.
Finally Lexus used a particular type of wheel nut which run parallel through the hole, other manufacturers use “tapered” nuts, using the wrong type can cause serious damage including the wheel coming off!