Only mask wearers test positive (CV+)

I saw this posted on, yes, Twitter from Telegram:

”CoVid deniers who don’t wear masks, don’t get tested. Which means that the increase in case numbers is mask wearers.”

Which fallacy is this? I’m assuming by leaving out the comma after the first “CoVid deniers...” he means that all deniers don’t wear masks nor do they get tested, although clear use of punctuation is not always a given in Tweets. I’ve added implied assumptions in A, C and D:

‪A- Some CoVid deniers don’t wear masks.‬
‪B- CoVid deniers who don’t wear masks don’t get tested.‬
‪C- There is an increase in case numbers from those who are tested.‬
‪D- Only mask wearers get tested.‬
‪E- Ergo, The increase in case numbers is only mask wearers.‬

it seems to be a valid argument yet still false. Where does it break down?

This is a problem, specifically, with sampling rather than logic. One can also argue it is a general problem with reason , because one doesn't need to be a social scientist to see the problem with the sample. If it were true that significantly more deniers refuse to get tested than non-deniers, this would skew the results of those tested positive.

I also question the assumptions here (i.e., truth of the premises). COVID doesn't pass those who deny it exists. In fact, I would bet that deniers get COVID at significantly higher rates that those who take proper precautions. Asymtomatic people are just as likely to be deniers as non-deniers, so unless there is a substantial group of deniers who are sick and refuse to get tested, the premise of this "argument" is baseless (I would ask for evidence of this).

Now let's look at the argument as you have it presented.

A&B are not necessary for the conclusion. The conclusion says nothing about COVID deniers, so we don't need those premises. Also, the entire argument is confusing and ambiguous as written, leaving out scope in a couple of places. All you need is

P1. The number of positive cases has increased.
P2. Only mask wearers are counted in positive cases.
C. Therefore, the increase in positive cases is due exclusively to mask wearers.

This is a valid argument, but not at all sound as I mentioned earlier.

I don't see a fallacy, only a statement of observation.  Your implied assumptions/consequences are good questions to ask the speaker, to see if he meant E.

The wearer may be simply more concerned, but the intention of the writer is legitimately challengeable imo.