It is not distortion in the usual sense. It sounds like ring mod maybe or yes the oscillator frequency itself could be modulated by another frequency. Filter might be getting some of this modulation source too.
There is hint of that metallic ring mod sound in there. It does not sound so much like an effect but it may be happening right at the source.
A modular synth will get you that sound. I am sure some of your synths will allow it. Some LFO's can run real fast too almost up in audio freq range. The modulation frequency is lower than you think though.