ah... they didn't fasten your hoses well enough, likely...

LOL, nangyari din sa akin yan dati... was having AC work done on my Sentra, and we couldn't finish the conversion, so we left the hoses off... after leaving the shop, I was driving down Buendia when suddenly white smoke started billowing out from under my hood? The disconnected compressor was spewing lots of oil onto the headers, creating clouds of smoke... a cool effect, but irritating nonetheless.

BTW, what did you have done to your AC at the shop?