I guess this is a clumsy attempt to say, "you think you're free, but you're not". I'm sure they have in mind "the truth shall set you free" (John 8:32). In the context of that verse, Jesus explains what freedom means: "he who sins is a slave to sin". Since by Biblical standards, we commit the sin of unbelief, then we are slaves to it.

The Bible is full of circular reasoning and sanctioned gaslighting like that. As well as assuming way too much about individual motivations and intents, and ascribing nefarious purpose where it doesn't exist.

In Fundamentalist World [tm], there are certain over-arching assumptions about life ... that we are acting out a sort of cosmic drama about sin and redemption, and people are animated, at least ultimately, by influencing good and evil spirits -- the best and worst "angels of our nature". So we are in thrall either to god and his angels or satan and his demons. And I daresay that many fundamentalists have way more respect for satan's wiles than for god's.

Intellectual freedom is the mortal enemy of authoritarian religion, so they never miss an opportunity to cast aspersions on it.