They probably let the air out of your tires if you were running high, or even recommended pressure.
Every mechanic would let air out of my tires even when I was running the factory recommended 38/38 in my I1... when I started running max sidewall, they would come running saying "whew, I fixed your car, it was about to blow up" and let it down to 30/30 or 32/32.
2004 Honda Civic Hybrid "Eeyore" @ 49 mpg
-MaxIMA, OBDIIC&C, IMAC&C, Lower grill block
RIP 2000 Insight, 40k miles @ 69.2 mpg
2000 Insight, AKA "The Basket Case" or "The Go Pod" @185k miles @ 63.5 mpg
-IMAC&C, OBDIIC&C, Scott's aero panel, grid charger, cheapo sound system