Usually when people talk about “the spectrum”, what they mean is “the autism spectrum” — but that’s not the only spectrum there is.
There is an obsessive-compulsive spectrum, a tic spectrum, a schizophrenia spectrum, and probably others I don’t know about yet. The interesting thing is that sometimes, even though these are separate spectrums, at times they seem to overlap.
For example; the “magical thinking” part of OCD resembles the “something special is meant for me” feeling characteristic of schizophrenia. It is often difficult to differentiate between tics and compulsions, thus blurring the OCD/tic spectrum. And, as far as autism, many people with OCD, tics, or schizophrenia feel a hint of the social difficulties and withdrawal that autistics have. Autistics also engage in repetitive/arranging behaviors, but for different motivational reasons than those with OC disorders.
I believe most psychological disorders (and maybe even some developmental ones) are an exaggeration of what is, in moderation, a normal and beneficial trait. So, perhaps it’s not so surprising that in way, they may all be connected.