diversifying is when you invest into different industries or markets. this guys is investing in the same building just using a different vehicle.

I don't think you have to have different industries or markets in order for it to be diversification. I think it's enough that the assets are not perfectly correlated.

Sorry but it just isn't diversification. If he wanted to diversify into property the reasonable course of action would be to buy properties that WeWork weren't renting in areas WeWork don't strongly impact the market. By investing into property rented by WeWork he's further concentrating his risk - not only is he invested in the company but now he's also invested in a property whose value is largely reliant on the rental income from WeWork. Technically his risk profile is slightly diversified - because part of his risk is now just in the property market it means his portfolio is more diverse than just being invested in WeWork, but it's significantly less diverse than what any reasonable person would have achieved by just investing in other properties. For that reason you can confidently say that he's not diversifying - but if his intention was diversifying this is almost THE least effective way of doing it.