I mean it shouldn't be that hard to understand. Housing prices skyrocketed when interest rates dropped during the pandemic. Add the effects of inflation, increases municipal evaluations leading to higher taxes, and you get more costs passed on to renters. This started before all the news of "HuGe SuRgE ImMiGrAnTs".
That being said there is still plenty of truth to the argument that if we do indeed want to welcome more people here, we better make sure there are affordable places to live. So the article addresses that better regulations are needed to ensure an adequate supply of affordable housing. BUT, if people already in Canada are really struggling to get affordable housing, and the number of people who need affordable housing is increasing, you can see why this might be a problem.