«وَقَدْ تُطْلَقُ الْمُتَابَعَةُ عَلَى الشَّاهِدِ، وَبِالْعَكْسِ»
Sometimes mutaba‘ah is used for a shahid, and vice versa.
The standard distinction turns on whether the same Companion transmits the report, but some hadith critics use “follow-up” more broadly for corroboration and “witness” for related supporting evidence. A looser use is not necessarily a contradiction.
Practical caution: when reading a critical assessment, examine the actual chains as well as the chosen term. Determine whether the companion is the same or different and exactly which feature of the report receives support.