They are acting childish, but they most likely do think you snubbed them. How could they not?
Tell them you're sorry it took you so long to get to their yard, but you all became sick with the flu. If you don't have their phone #, ask for it and say you can use it to call them and explain if it happens again.
Tell them you're sorry it took you so long to get to their yard, but you all became sick with the flu. If you don't have their phone #, ask for it and say you can use it to call them and explain if it happens again.