Yes, by definition a recession would reduce total sales. But it wouldn't reduce sales evenly across all manufacturers. One car maker is not sales constrained (guess who) and there is no guarantee a recession would cause them to be sales constrained. The kind of person that retained their job through a recession is already the kind of person more likely to buy a Tesla. Recessions do not cause car sales to cease, not even close. Recessions hit companies that are sales constrained the hardest because the slightest dent in the economy reduces sales and therefore profits.
What was the hit to the overall automotive market during the last recession, 40%? Even if Tesla significantly outpaced the industry, lets say they only saw a 20% reduction in demand, do you not think that could have an impact? New car sales have a very elastic demand, they get hammered in economic hard times.
Now, granted, this argument is quite silly. The likely hood of a recession the likes we saw in 2008 happening now are slim to none. The only real default risk out there right now is student loans, and that has existed for a while. And the virus, well, it's either going to be contained or spread to the point where quarantines become unnecessary and we will just go about our lives. And even if such a recession happened, there are so many other factors that would impact how Tesla and the automotive industry in general fare, it's really impossible to just make blanket statements.