i mean i got what he was saying but it makes an awkward statement as well as not the correct quote reference.
The "probably is" refers to the 'seems too good to be true", meaning it probably is too good to be true. the way he has it written forces you to split it out and look at only the true which is kinda fumbly.
someone with better knowledge of english parts of speech could weigh in on why it needs to be one way or the other but the original quote does use an 'is' so that's all i was pointing out.
either way, i knew what he was going for but it caused a logic stumble on first read of that sentence.