Q: New tires yesterday and later my brake light came on. Pedal pressure lost, then came back, light still on! 99 Buick Century

Yesterday I went to a chain tire store for 2 new tires in the front and an oil change. I have ABS. When they drove me to the bank the tech mentioned I had a cracked brake line but he didn't seem too concerned about it, like it was an afterthought. About 6 hours later my brake light came on but pedal pressure was still there. Later when I parked, I lost all pedal pressure. I heard a weird noise or vibration that sounded like a pump emptying still running after the turned the car off. When I came back, there was a fluid beneath my engine. Pedal pressure came back but the light is still on. I checked the brake fluid reservoir and it looks low but there is fluid there.

Weird thing: Something like this happened 6-18 months ago. Can't remember what I was having done, but afterwords I had lost most of my brake fluid. I went back to the mechanic and he claimed to have no idea. We refilled the brake fluid and I never had problems after that.

Whats going on?!? Who's responsible?

My car has 125000 miles.
My car has an automatic transmission.