How did person X get the birdemic?

No mystery At All. 

The birdemic is a respiratory virus, therefore its spread cannot be stopped (only, perhaps, a little delayed). 

So everybody will be exposed to it sooner or later, until herd immunity is established and a sufficient proportion of people are immune so that the virus will (essentially) die-out*. 

So exposure of healthy and young people (young = children, adolescents, young adults and the middle aged - none of whom are significantly at risk) is A Good Thing.

It is a Good Thing (and necessary) that the majority of young/ middle aged/ healthy people are exposed to the birdemic, and either get the birdemic; or (and this is the large majority) either become immune without being seriously ill, or else are already immune to it (presumably from cross-immunity with a previous similar infection). 

And the longer that exposure to the birdemic by the mass majority is delayed; the more among the elderly/already-sick people will be exposed, and will die.  

Nothing strange, nothing mysterious, nothing specially serious to see here: move along...

(But of course It's Not About The Birdemic; it is about the response; which Just Happens to be the exact same 'Great Reset' response recommended to prevent Global Warming and cure Systemic Racism (and QWERTY-phobia, natch): ie. Nearly everybody Needs to stay indoors, in a room, preferably alone, essentially all of the time, forever.)   

*This is how every single pandemic in the history of mankind has died-out and ceased to be a pandemic. The birdemic is just a normal respiratory virus like flu, with normal levels of mortality (c.1:2000 population, everywhere with comparable data collection and population structure) and morbidity (levels of sickness) among the usual kinds of people (i.e. nearly all the deaths are among the very old, especially those beyond the biological lifespan; and those already chronically and seriously ill).