The original quote spoke of "twice been stripped naked and searched, eleven times been handcuffed, and five times been locked up in different holding cells" - which is unpleasant treatment, but probably not hugely different from the treatment of many prisoners, fairly regularly, within our dehumanising criminal justice system. And I don't think it would constitute torture, per your definition.
That said, as another commenter added, he's apparently been in solitary confinement [for up to 23 hours a day[0] ] in a high category prison for a year. This sounds pretty awful, and much closer to a definition of "torture". That said, it's hard to know: maybe prisoners of his nature are routinely interned in Belmarsh? And maybe being in your cell for 23 hours a day is routine for prisoners in Belmarsh?
Would be interesting to know why it's taken a year for his case to be heard, though.
[0] https://inews.co.uk/news/julian-assange-solitary-confinement...