Presumably the heretics were blaspheming the angels, since this is mentioned in Jude 8. In this case they may have considered themselves to be above the angels, stronger than the angels, or claiming that the angels were not worthy of respect. Alternatively, Jude is simply saying that the false teachers are blaspheming the truth of God (Jude 1:4), a truth which they do not comprehend despite their claims.
10 But these people blaspheme all that they do not understand, and they are destroyed by all that they, like unreasoning animals, understand instinctively.