If this happens then that happens fallacy

Well I guess it could be if it's based on an actual argument which he is misrepresenting, though typically a straw man would take the form of misrepresenting the original argument by inference e.g. 

Mark says that the limit of alcohol allowed for drivers isn't low enough.

Gary responds that it would be crazy to relax the drink drive limit as some people are effected more severely by alcohol and would be out of control and high risk.

Here we can infer that Gary is responding to an argument which Mark didn't make. Because Mark wanted the limit  lowered it may sound as though this is a relaxation of the limit of you don't take pause and examine this properly. Thus it is a straw man as it could fool some people who observed the exchange. 

As to your friend's argument, it is just asserted without any rationale, so I would say that it's a n on sequitur; it does not follow that it will accomplish any such thing.

Going to the pharmacy doesn't involve sitting in close proximity to people for hours on end, in an enclosed environment with lots of shared surfaces.

Going to the pharmacy doesn't have to be within a specific timeframe which forces large numbers to be present at the same time. 

And going to the pharmacy isn't the only way to obtain a face mask. 

Its not a strawman unless he was distorting someone else argument. 

It doesn't even make sense to me, what do airplanes have to do with pharmacies? Is the assumption here that masks are only sold at pharmacies? In any case, this is more of a claim or opinion. We can assume a "therefore, they should not make masks a requirement on planes," and a "mass gathers at pharmacies is bad," but still, we have an unsupported claim that neglects to provide a reason why mandatory masks on planes will lead to crowded pharmacies.