How can it be said that all the Companions are trustworthy, while there are verses describing the Bedouins (who are part of the Companions) as "most severe in disbelief and hypocrisy"?

The justice of the Companions is a matter of consensus among the Salaf. Those Bedouins who were hypocrites and disbelievers, who embraced Islam outwardly but did not believe in their hearts, are not included in the definition of a Companion. As for those among them who truly believed, they are the just Companions. Allah Almighty distinguished in His Book between the disbelieving and hypocritical Bedouins and the believing Bedouins.