3,000 clients. They must have a staff of hundreds.
Not all of them are there at once.
You have a point but do you realize that they've been open since July 2007 and that averages to 1,000 new clients a year which means that they have an average of two and a half new clients everyday 365 days a year.
I'm guessing they count every person who has ever boarded with them....
Although, having run a boarding kennel, I would consider 'clients' the regular repeat customers, the ones you get to know. Otherwise, they are simply customers, to me.