What is this “working interview” scheme & why did I just work 4.5 hours only to be told “we have one more candidate tomorrow, well let you know”?

I’ve never heard of a working interview before this job at a dog facility. I felt great while working but when they told me at the end they’ll let me know… it makes me question Will I get the job? Am I going to get paid (this happened in Texas)? I thought for sure I’d get the job because they were very accommodating to me when I had to have surgery 2 weeks ago & kept on asking when I’d be better so I could do this “working interview”.