If this is true then Mathew should put Radio Cristiandad in the same category as Traditio. Whatever Bp Williamson's secular views may be he is solid on matters of the Faith. Because he wouldn't budge he was kicked out by Fellay.
Radio Cristiandad does not attack systematically Bp. Williamson. In fact, you can see some of the bishop's writings published there. However, I must point out that some of Bp. Williamson's attitudes and assertions have been questioned and criticized by some priests, and some of these critics have been published as well, as can be seen
here.