I've looked into this logically,,, IMO speculation or theory is just that I have looked more to the word Prison. IMO the word Observants or watch the plural form of prison is more fitting when used in its Greek or Hebrew plural form in the context of the verses used when explaining what John doing while his disciples were speaking to Him about Jesus and this is before the baptism of Jesus when John had not seen Jesus yet.. IMO
Shamar or Mishmar being the orginal word and Prison being the translated word of it..
KJV
Strong's Concordance
mishmar: place of confinement, jail, prison, guard, watch, observance
Original Word: מִשְׁמָר
Part of Speech: Noun Masculine
Transliteration: mishmar
Phonetic Spelling: (mish-mawr')
Short Definition: guard
NAS Exhaustive Concordance
Word Origin
from shamar
Definition
place of confinement, jail, prison, guard, watch, observance
NASB Translation
confinement (4), custody (2), diligence (1), division (2), guard (8), keeping watch (1), post (1), prison (1), prison* (1), services (1).
Since Luke 7:18 on is the same as Matthew 11:2 on
Lk7:18 John's disciples told him about all these things. Calling two of them,
Mt11:2 When John heard in Observants of what Christ was doing, he sent his disciples
Mt11:3 to ask him, "Are you the one who was to come, or should we expect someone else?"
Mt11:4 Jesus replied, "Go back and report to John what you hear and see:
Mt11:5 The blind receive sight, the lame walk, those who have leprosy are cured, the deaf hear, the dead are raised, and the good news is preached to the poor.
Mt11:6 Blessed is the man who does not fall away on account of me."