Wannago the virus is aerosolised, it spreads in droplets of moisture in the air. Have a look at dr John Campbell on YouTube, he explains and references a study where a man got on a bus and infected someone sitting 4.5 metres behind him.
But distance does matter (and note that due to the physics of inertia, a stopping and starting bus is a different scenario to a non moving environment). It is important to understand which activities are more and less risky. The further away you are from another person, the safer you are. Which is why the hot yoga may be, if it is done in a safe way, at two metres apart, far less risky than having coffee, where the normal distance between people is less than a metre.
Now the government guidance is that even that risk, of going out at all, is too great for those who are vulnerable, the elderly and those with underlying conditions. That might be extended to those who are living with those with underlying conditions, For those who do not fit into either of those categories, what has been asked is social distancing (which you cannot do in a pub or restuarant, which is designed for close contact). It may however, be possible and a sensible risk to take to do hot yoga, if one is not in a high risk category, not likely now to meet someone in a high risk category (they are all at home), and a two metre distance is maintained. Far more sensible a risk than the coffee afterwards.
The "hot" bit of hot yoga might also be interesting. Some people seem to think that this virus doesn't like heat, and that we might therefore have a breather if /when we get a heat wave, while others don't think that is the case, and the summer will make no difference. If in fact the virus is not immune to heat, it might spread less and stay on surfaces less in a hot yoga class, assuming hot means over say 28 degrees, than out in the park, making it actually slightly safer, if the same distancing is maintained than outside.
If you ratchet all options up as maximum risk, then you prevent people making reasonable assessments and cutting down on more risky behaviours rather than less, because you have told them the risks are the same, even when they aren't. And you prevent them taking precautions (eg going to hot yoga but keeping far away), rather than saying it is all forbidden, meaning if they go, they are less likely to spread out.