The literal force of «كَذَبَ» is “he lied”; it must not be silently weakened to “he was unreliable.” Equally, each such rebuke does not, without further evidence, establish deliberate fabrication of every report.
Al-Nawawī describes Ṣāliḥ al-Murrī (Ṣāliḥ b. Bashīr) as known for worship and ascetic devotion, yet such piety does not establish technical reliability in hadith. An unskilled narrator might repeat material without discerning its truth and thereby report something false without deliberately inventing it. Personal devotion and proven precision in transmission must be assessed separately.