Maybe Burt knows a bit more about Radon Labs because ...
either a) Shirley once worked there; she died of cancer if my memories about her death are right; maybe there is a link between her death and her work; and probably she told Burt about what she did in Radon Labs and how some things in Radon Labs worked or were organized;
or/and b) some of Burt's regular customers worked at Radon Labs and they got into some chatter about this and that; and maybe it was through such chatter that Burt put together some pieces, so now he has a basic understanding of some stuff regarding the laboratiers - like for example the various ranks of the scientific or security personell and stuff ...

Best wishes!
Liam